diff --git a/alien.py b/alien.py
new file mode 100644
index 0000000..d4ee7b0
--- /dev/null
+++ b/alien.py
@@ -0,0 +1,39 @@
+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初始位置"""
+        super().__init__()
+        self.screen = screen
+        self.ai_settings = ai_settings
+
+        # 加载外星人头像，并设置其rect值
+        self.image = pygame.image.load("./images/alien.bmp")
+        self.rect = self.image.get_rect()
+
+        # 每个外星人起初都在屏幕的左上角附近
+        self.rect.x = self.rect.width
+        self.rect.y = self.rect.height
+
+        # 存储外星人的具体位置
+        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，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