diff --git a/alien.py b/alien.py
new file mode 100644
index 0000000..91061b6
--- /dev/null
+++ b/alien.py
@@ -0,0 +1,88 @@
+import pygame
+from pygame.sprite import Sprite
+
+
+class Alien(Sprite):
+    """表示单个外星人的类"""
+
+    def __init__(self, ai__settings, screen):
+        """初始化外星人并设置其起始位置"""
+        super(Alien, self).__init__()
+        self.screen = screen
+        self.ai_settings = ai__settings
+
+        # 加载外星人图像，并设置其rect属性
+        self.image = pygame.image.load('images/alien.png')
+        self.rect = self.image.get_rect()
+        # 每个外星人最初都在屏幕左上角附件
+        self.rect.x = self.rect.width
+        self.rect.y = self.rect.height
+        # 储存外星人的准确位置
+        self.x = float(self.rect.x)
+
+    def blitme(self):
+        """在指定位置绘制外星人"""
+        self.screen.blit(self.image, self.rect)
+
+    def check_edges(self):
+        """如果外星人位于屏幕边缘，就返回True"""
+        screen_rect = self.screen.get_rect()
+        if self.rect.right >= screen_rect.right:
+            return True
+        elif self.rect.left <= 0:
+            return True
+
+    def update(self):
+        """向左或向右移动外星人"""
+        self.x += (self.ai_settings.alien_speed_factor * self.ai_settings.fleet_direction)
+        self.rect.x = self.x
+
+
+class BossAlien(Sprite):
+    """BOSS外星人"""
+
+    def __init__(self, ai_settings, screen, health=500):
+        """初始化外星人并设置其初始位置"""
+        self.screen = screen
+        self.ai_settings = ai_settings
+        self.health = health
+
+        # 加载外星人图像，并设置其rect属性
+        self.image = pygame.image.load('images/bossalien.png')
+        self.rect = self.image.get_rect()
+        self.screen_rect = screen.get_rect()
+
+        self.rect.x = 550
+        self.rect.y = 100
+
+        # 储存外星人的精准位置
+        self.x = float(self.rect.x)
+
+    # 设置生命值
+    # health=100
+
+    def blitme(self):
+        """在指定位置绘制外星人"""
+        self.screen.blit(self.image, (self.rect.x, self.rect.y))
+
+    def draw_health_bar(self, screen):
+        """显示血条"""
+        # 参数依次表示：在screen上面绘制，颜色，（改图案左上角的坐标，长度和高度）
+
+        # 灰色的空白血条
+        pygame.draw.rect(screen, (0, 230, 0), ((380, 100), (500, 10)))
+        # 红色的现有血条
+        pygame.draw.rect(screen, (255, 0, 0), ((380, 100), (self.health, 10)))
+
+    def check_edges(self):
+        """如果外星人位于屏幕边缘就返回True"""
+        screen_rect = self.screen.get_rect()
+        if self.rect.right >= screen_rect.right:
+            return True
+        elif self.rect.left <= 0:
+            return True
+
+    def update(self):
+        """向左向右移动外星人"""
+        self.x += (self.ai_settings.alien_speed_factor * self.ai_settings.bossalien_direction)
+        self.rect.x = self.x