diff --git a/README.md b/README.md
index 1aca2d3..9afe796 100644
--- a/README.md
+++ b/README.md
@@ -1,15 +1,33 @@
-PythonShootGame
-===============
+# PythonShootGame
 
-A simple shoot game by python
+A simple shoot game written in Python.
 
+# Introduction
 
 This project only include two simple .py files: 
 
-  mainGame.py：the initialization and main loop of the game
-  
-  gameRole.py: class of the game role
+1. mainGame.py: The initialization and main loop of the game.
+2. gameRole.py: Class of the game role.
+
+# Requirement
+
+1. Python 2.7
+2. Python-Pygame
   
+# How To Start Game
   
-To run this game, first install python 2.7, then install the corresponding version of pygame.
-After that, double click the mainGame.py, you can play it.
+```bash
+$ python mainGame.py
+```
+
+# License
+GPL
+
+# Screeshot
+
+![](http://s2.postimg.org/728c1wy4p/Screenshot_5.png)
+
+![](http://s30.postimg.org/fflxcv9ld/Screenshot_6.png)
+
+# Doc
+[使用Pygame制作微信打飞机游戏PC版](https://www.cnblogs.com/dukeleo/p/3339780.html) (a Chinese startup)
diff --git a/mainGame.py b/mainGame.py
index 17427df..91df38f 100644
--- a/mainGame.py
+++ b/mainGame.py
@@ -77,7 +77,7 @@
 
 while running:
     # 控制游戏最大帧率为60
-    clock.tick(60)
+    clock.tick(45)
 
     # 控制发射子弹频率,并发射子弹
     if not player.is_hit:
@@ -113,7 +113,7 @@
             player.is_hit = True
             game_over_sound.play()
             break
-        if enemy.rect.top < 0:
+        if enemy.rect.top > SCREEN_HEIGHT:
             enemies1.remove(enemy)
 
     # 将被击中的敌机对象添加到击毁敌机Group中，用来渲染击毁动画
@@ -129,9 +129,9 @@
     if not player.is_hit:
         screen.blit(player.image[player.img_index], player.rect)
         # 更换图片索引使飞机有动画效果
-        player.img_index = shoot_frequency / 8
+        player.img_index = shoot_frequency // 8
     else:
-        player.img_index = player_down_index / 8
+        player.img_index = player_down_index // 8
         screen.blit(player.image[player.img_index], player.rect)
         player_down_index += 1
         if player_down_index > 47:
@@ -145,7 +145,7 @@
             enemies_down.remove(enemy_down)
             score += 1000
             continue
-        screen.blit(enemy_down.down_imgs[enemy_down.down_index / 2], enemy_down.rect)
+        screen.blit(enemy_down.down_imgs[enemy_down.down_index // 2], enemy_down.rect)
         enemy_down.down_index += 1
 
     # 绘制子弹和敌机
@@ -194,4 +194,4 @@
         if event.type == pygame.QUIT:
             pygame.quit()
             exit()
-    pygame.display.update()
\ No newline at end of file
+    pygame.display.update()