diff --git a/en/src/SUMMARY.md b/en/src/SUMMARY.md
index d0facbc..9921720 100644
--- a/en/src/SUMMARY.md
+++ b/en/src/SUMMARY.md
@@ -55,7 +55,7 @@
   - [advanced](lifetime/advance.md)
 - [Functional programing](functional-programing/intro.md)
   - [Closure](functional-programing/cloure.md)
-  - [Iterator TODO](functional-programing/iterator.md)
+  - [Iterator](functional-programing/iterator.md)
 - [newtype and Sized TODO](newtype-sized.md)
 - [Smart pointers TODO](smart-pointers/intro.md)
   - [Box](smart-pointers/box.md)
diff --git a/en/src/functional-programing/cloure.md b/en/src/functional-programing/cloure.md
index 8df7250..7546057 100644
--- a/en/src/functional-programing/cloure.md
+++ b/en/src/functional-programing/cloure.md
@@ -186,7 +186,7 @@ fn exec<'a, F: __>(mut f: F)  {
 }
 ```
  
-#### How does the compiler determine the trait
+#### Which trait does the compiler prefer to use?
 - Fn: the closure uses the captured value by reference (&T)
 - FnMut: the closure uses the captured value by mutable reference (&mut T)
 - FnOnce: the closure uses the captured value by value (T)
diff --git a/en/src/functional-programing/iterator.md b/en/src/functional-programing/iterator.md
index 641413e..0a49c37 100644
--- a/en/src/functional-programing/iterator.md
+++ b/en/src/functional-programing/iterator.md
@@ -1,21 +1,329 @@
 # Iterator
+The iterator pattern allows us to perform some tasks on a sequence of items in turn. An iterator is responsible for the logic of iterating over each item and determining when the sequence has finished.
 
-https://doc.rust-lang.org/stable/rust-by-example/flow_control/for.html#for-and-iterators
+## for and iterator
+```rust
+fn main() {
+    let v = vec![1, 2, 3];
+    for x in v {
+        println!("{}",x)
+    }
+}
+```
 
+In above code, You may consider `for` as a simple loop, but actually it is iterating over a iterator. 
+
+By default  `for` will apply the `into_iter` to the collection, and change it into a iterator. As a result, the following code is equivalent to previous one:
+```rust
+fn main() {
+    let v = vec![1, 2, 3];
+    for x in v.into_iter() {
+        println!("{}",x)
+    }
+}
+```
+
+1、🌟
 ```rust,editable
-// (all the type annotations are superfluous)
-// A reference to a string allocated in read only memory
-let pangram: &'static str = "the quick brown fox jumps over the lazy dog";
-println!("Pangram: {}", pangram);
+/* Refactoring the following code using iterators */
+fn main() {
+    let arr = [0; 10];
+    for i in 0..arr.len() {
+        println!("{}",arr[i])
+    }
+}
+```
 
-// Iterate over words in reverse, no new string is allocated
-println!("Words in reverse");
-for word in pangram.split_whitespace().rev() {
-    println!("> {}", word);
+2、 🌟 One of the easiest ways to create an iterator is to use the range notion: `a..b`.
+```rust,editble
+/* Fill in the blank */
+fn main() {
+    let mut v = Vec::new();
+    for n in __ {
+       v.push(n);
+    }
+
+    assert_eq!(v.len(), 100);
+}
+```
+
+## next method
+All iterators implement a trait named `Iterator` that is defined in the standard library:
+```rust
+pub trait Iterator {
+    type Item;
+
+    fn next(&mut self) -> Option<Self::Item>;
+
+    // methods with default implementations elided
+}
+```
+
+And we can call the `next` method on iterators directly.
+
+3、🌟🌟
+```rust,editable
+/* Fill the blanks and fix the errors.
+Using two ways if possible */
+fn main() {
+    let v1 = vec![1, 2];
+
+    assert_eq!(v1.next(), __);
+    assert_eq!(v1.next(), __);
+    assert_eq!(v1.next(), __);
+}
+```
+
+## into_iter, iter and iter_mut
+In the previous section, we have mentioned that `for` will apply the `into_iter` to the collection, and change it into a iterator.However, this is not the only way to convert collections into iterators.
+
+`into_iter`, `iter`, `iter_mut`, all of them can convert an collection into iterator, but in different ways.
+
+- `into_iter` cosumes the collection, once the collection has been comsumed, it is no longer available for reuse, because its ownership has been moved within the loop.
+- `iter`, this borrows each element of the collection through each iteration, thus leaving the collection untouched and available for reuse after the loop
+- `iter_mut`, this mutably borrows each element of the collection, allowing for the collection to be modified in place.
+
+4、🌟
+```rust,editable
+/* Make it work */
+fn main() {
+    let arr = vec![0; 10];
+    for i in arr {
+        println!("{}", i)
+    }
+
+    println!("{:?}",arr);
+}
+```
+
+5、🌟
+```rust,editable
+/* Fill in the blank */
+fn main() {
+    let mut names = vec!["Bob", "Frank", "Ferris"];
+
+    for name in names.__{
+        *name = match name {
+            &mut "Ferris" => "There is a rustacean among us!",
+            _ => "Hello",
+        }
+    }
+
+    println!("names: {:?}", names);
+}
+```
+
+6、🌟🌟
+```rust,editable
+/* Fill in the blank */
+fn main() {
+    let mut values = vec![1, 2, 3];
+    let mut values_iter = values.__;
+
+    if let Some(v) = values_iter.__{
+        __
+    }
+
+    assert_eq!(values, vec![0, 2, 3]);
+}
+```
+
+
+## Creating our own iterator
+We can not only create iterators from collections types, but also can create iterators by implementing the `Iterator` trait on our own types.
+
+**Example**
+```rust
+struct Counter {
+    count: u32,
 }
 
-// Copy chars into a vector, sort and remove duplicates
-let mut chars: Vec<char> = pangram.chars().collect();
-chars.sort();
-chars.dedup();
+impl Counter {
+    fn new() -> Counter {
+        Counter { count: 0 }
+    }
+}
+
+impl Iterator for Counter {
+    type Item = u32;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        if self.count < 5 {
+            self.count += 1;
+            Some(self.count)
+        } else {
+            None
+        }
+    }
+}
+
+fn main() {
+    let mut counter = Counter::new();
+
+    assert_eq!(counter.next(), Some(1));
+    assert_eq!(counter.next(), Some(2));
+    assert_eq!(counter.next(), Some(3));
+    assert_eq!(counter.next(), Some(4));
+    assert_eq!(counter.next(), Some(5));
+    assert_eq!(counter.next(), None);
+}
+```
+
+7、🌟🌟🌟
+```rust,editable
+struct Fibonacci {
+    curr: u32,
+    next: u32,
+}
+
+// Implement `Iterator` for `Fibonacci`.
+// The `Iterator` trait only requires a method to be defined for the `next` element.
+impl Iterator for Fibonacci {
+    // We can refer to this type using Self::Item
+    type Item = u32;
+    
+    /* Implement next method */
+    fn next(&mut self)
+}
+
+// Returns a Fibonacci sequence generator
+fn fibonacci() -> Fibonacci {
+    Fibonacci { curr: 0, next: 1 }
+}
+
+fn main() {
+    let mut fib = fibonacci();
+    assert_eq!(fib.next(), Some(1));
+    assert_eq!(fib.next(), Some(1));
+    assert_eq!(fib.next(), Some(2));
+    assert_eq!(fib.next(), Some(3));
+    assert_eq!(fib.next(), Some(5));
+}
+```
+
+## Methods that Consume the Iterator
+The `Iterator` trait has a number of methods with default implementations provided by the standard library.
+
+
+### Consuming adaptors
+Some of these methods call the method `next`to use up the iterator, so they are called *consuming adaptors*.
+
+8、🌟🌟
+```rust,edtiable
+/* Fill in the blank and fix the errors */
+fn main() {
+    let v1 = vec![1, 2, 3];
+
+    let v1_iter = v1.iter();
+
+    // The sum method will take the ownership of the iterator and iterates through the items by repeatedly calling next method
+    let total = v1_iter.sum();
+
+    assert_eq!(total, __);
+
+    println!("{:?}, {:?}",v1, v1_iter);
+}
+```
+
+
+#### collect
+Other than converting a collection into an iterator, we can also `collect` the result values into a collection, `collect` will cosume the iterator.
+
+9、🌟🌟
+```rust,editable
+/* Make it work */
+use std::collections::HashMap;
+fn main() {
+    let names = [("sunface",18), ("sunfei",18)];
+    let folks: HashMap<_, _> = names.into_iter().collect();
+
+    println!("{:?}",folks);
+
+    let v1: Vec<i32> = vec![1, 2, 3];
+
+    let v2 = v1.iter().collect();
+
+    assert_eq!(v2, vec![1, 2, 3]);
+}
+```
+
+
+###  Iterator adaptors
+Methods allowing you to change one iterator into another iterator are known as *iterator adaptors*. You can chain multiple iterator adaptors to perform complex actions in a readable way.
+
+But beacuse **all iterators are lazy**, you have to call one of the consuming adapers to get results from calls to iterator adapters.
+
+10、🌟🌟
+```rust,editable
+/* Fill in the blanks */
+fn main() {
+    let v1: Vec<i32> = vec![1, 2, 3];
+
+    let v2: Vec<_> = v1.iter().__.__;
+
+    assert_eq!(v2, vec![2, 3, 4]);
+}
+```
+
+11、🌟🌟
+```rust
+/* Fill in the blanks */
+use std::collections::HashMap;
+fn main() {
+    let names = ["sunface", "sunfei"];
+    let ages = [18, 18];
+    let folks: HashMap<_, _> = names.into_iter().__.collect();
+
+    println!("{:?}",folks);
+}
+```
+
+
+#### Using closures in iterator adaptors
+
+12、🌟🌟 
+```rust
+/* Fill in the blanks */
+#[derive(PartialEq, Debug)]
+struct Shoe {
+    size: u32,
+    style: String,
+}
+
+fn shoes_in_size(shoes: Vec<Shoe>, shoe_size: u32) -> Vec<Shoe> {
+    shoes.into_iter().__.collect()
+}
+
+fn main() {
+    let shoes = vec![
+        Shoe {
+            size: 10,
+            style: String::from("sneaker"),
+        },
+        Shoe {
+            size: 13,
+            style: String::from("sandal"),
+        },
+        Shoe {
+            size: 10,
+            style: String::from("boot"),
+        },
+    ];
+
+    let in_my_size = shoes_in_size(shoes, 10);
+
+    assert_eq!(
+        in_my_size,
+        vec![
+            Shoe {
+                size: 10,
+                style: String::from("sneaker")
+            },
+            Shoe {
+                size: 10,
+                style: String::from("boot")
+            },
+        ]
+    );
+}
 ```
\ No newline at end of file
diff --git a/solutions/functional-programing/iterator.md b/solutions/functional-programing/iterator.md
new file mode 100644
index 0000000..f13dfb9
--- /dev/null
+++ b/solutions/functional-programing/iterator.md
@@ -0,0 +1,238 @@
+1、
+```rust
+fn main() {
+    let arr = [0; 10];
+    for i in arr {
+        println!("{}", i)
+    }
+}
+```
+
+2、
+```rust
+fn main() {
+    let mut v = Vec::new();
+    for n in 1..101 {
+       v.push(n);
+    }
+
+    assert_eq!(v.len(), 100);
+}
+```
+
+3、
+```rust
+fn main() {
+    let v1 = vec![1, 2];
+
+    // moving ownership
+    let mut v1_iter = v1.into_iter();
+
+    assert_eq!(v1_iter.next(), Some(1));
+    assert_eq!(v1_iter.next(), Some(2));
+    assert_eq!(v1_iter.next(), None);
+}
+```
+
+```rust
+fn main() {
+    let v1 = vec![1, 2];
+
+    // borrowing
+    let mut v1_iter = v1.iter();
+
+    assert_eq!(v1_iter.next(), Some(&1));
+    assert_eq!(v1_iter.next(), Some(&2));
+    assert_eq!(v1_iter.next(), None);
+}
+```
+
+4、
+```rust
+fn main() {
+    let arr = vec![0; 10];
+    for i in arr.iter() {
+        println!("{}", i)
+    }
+
+    println!("{:?}",arr);
+}
+```
+
+5、
+```rust
+fn main() {
+    let mut names = vec!["Bob", "Frank", "Ferris"];
+
+    for name in names.iter_mut() {
+        *name = match name {
+            &mut "Ferris" => "There is a rustacean among us!",
+            _ => "Hello",
+        }
+    }
+
+    println!("names: {:?}", names);
+}
+```
+
+6、
+```rust
+fn main() {
+    let mut values = vec![1, 2, 3];
+    let mut values_iter = values.iter_mut();
+
+    if let Some(v) = values_iter.next() {
+        *v = 0;
+    }
+
+    assert_eq!(values, vec![0, 2, 3]);
+}
+```
+
+7、
+```rust
+struct Fibonacci {
+    curr: u32,
+    next: u32,
+}
+
+// Implement `Iterator` for `Fibonacci`.
+// The `Iterator` trait only requires a method to be defined for the `next` element.
+impl Iterator for Fibonacci {
+    // We can refer to this type using Self::Item
+    type Item = u32;
+    
+    // Here, we define the sequence using `.curr` and `.next`.
+    // The return type is `Option<T>`:
+    //     * When the `Iterator` is finished, `None` is returned.
+    //     * Otherwise, the next value is wrapped in `Some` and returned.
+    // We use Self::Item in the return type, so we can change
+    // the type without having to update the function signatures.
+    fn next(&mut self) -> Option<Self::Item> {
+        let new_next = self.curr + self.next;
+
+        self.curr = self.next;
+        self.next = new_next;
+
+        // Since there's no endpoint to a Fibonacci sequence, the `Iterator` 
+        // will never return `None`, and `Some` is always returned.
+        Some(self.curr)
+    }
+}
+
+// Returns a Fibonacci sequence generator
+fn fibonacci() -> Fibonacci {
+    Fibonacci { curr: 0, next: 1 }
+}
+
+fn main() {
+    let mut fib = fibonacci();
+    assert_eq!(fib.next(), Some(1));
+    assert_eq!(fib.next(), Some(1));
+    assert_eq!(fib.next(), Some(2));
+    assert_eq!(fib.next(), Some(3));
+    assert_eq!(fib.next(), Some(5));
+}
+```
+
+8、
+```rust
+fn main() {
+    let v1 = vec![1, 2, 3];
+
+    let v1_iter = v1.iter();
+
+    // The sum method will take the ownership of the iterator and iterates through the items by repeatedly calling next method
+    let total: i32 = v1_iter.sum();
+
+    assert_eq!(total, 6);
+
+    println!("{:?}",v1);
+}
+```
+
+9、
+```rust
+use std::collections::HashMap;
+fn main() {
+    let names = [("sunface",18), ("sunfei",18)];
+    let folks: HashMap<_, _> = names.into_iter().collect();
+
+    println!("{:?}",folks);
+
+    let v1: Vec<i32> = vec![1, 2, 3];
+
+    let v2: Vec<_> = v1.into_iter().collect();
+
+    assert_eq!(v2, vec![1, 2, 3]);
+}
+```
+
+10、
+```rust
+fn main() {
+    let v1: Vec<i32> = vec![1, 2, 3];
+
+    let v2: Vec<_> = v1.iter().map(|x| x + 1).collect();
+
+    assert_eq!(v2, vec![2, 3, 4]);
+}
+```
+
+11、
+```rust
+use std::collections::HashMap;
+fn main() {
+    let names = ["sunface", "sunfei"];
+    let ages = [18, 18];
+    let folks: HashMap<_, _> = names.into_iter().zip(ages.into_iter()).collect();
+
+    println!("{:?}",folks);
+}
+```
+
+12、
+```rust
+#[derive(PartialEq, Debug)]
+struct Shoe {
+    size: u32,
+    style: String,
+}
+
+fn shoes_in_size(shoes: Vec<Shoe>, shoe_size: u32) -> Vec<Shoe> {
+    shoes.into_iter().filter(|s| s.size == shoe_size).collect()
+}
+
+fn main() {
+    let shoes = vec![
+        Shoe {
+            size: 10,
+            style: String::from("sneaker"),
+        },
+        Shoe {
+            size: 13,
+            style: String::from("sandal"),
+        },
+        Shoe {
+            size: 10,
+            style: String::from("boot"),
+        },
+    ];
+
+    let in_my_size = shoes_in_size(shoes, 10);
+
+    assert_eq!(
+        in_my_size,
+        vec![
+            Shoe {
+                size: 10,
+                style: String::from("sneaker")
+            },
+            Shoe {
+                size: 10,
+                style: String::from("boot")
+            },
+        ]
+    );
+}
+```
\ No newline at end of file