diff --git a/classical-encryption/monoalphabetic_cipher.py b/classical-encryption/monoalphabetic_cipher.py
new file mode 100644
index 0000000..6f2e8a0
--- /dev/null
+++ b/classical-encryption/monoalphabetic_cipher.py
@@ -0,0 +1,134 @@
+"""
+单表替换密码 (Monoalphabetic Cipher)
+实现字母表的随机替换加密
+"""
+
+import random
+import string
+
+
+def generate_key():
+    """
+    生成随机替换密钥
+    返回: 字典，包含字母到替换字母的映射
+    """
+    alphabet = list(string.ascii_uppercase)
+    shuffled = alphabet.copy()
+    random.shuffle(shuffled)
+    
+    key = {}
+    for i, char in enumerate(alphabet):
+        key[char] = shuffled[i]
+        key[char.lower()] = shuffled[i].lower()
+    
+    return key
+
+
+def monoalphabetic_encrypt(text, key):
+    """
+    单表替换加密
+    
+    Args:
+        text: 要加密的文本
+        key: 替换密钥字典
+    
+    Returns:
+        加密后的文本
+    """
+    encrypted_text = ""
+    
+    for char in text:
+        if char in key:
+            encrypted_text += key[char]
+        else:
+            encrypted_text += char
+    
+    return encrypted_text
+
+
+def monoalphabetic_decrypt(text, key):
+    """
+    单表替换解密
+    
+    Args:
+        text: 要解密的文本
+        key: 替换密钥字典
+    
+    Returns:
+        解密后的文本
+    """
+    # 创建反向密钥
+    reverse_key = {v: k for k, v in key.items()}
+    
+    decrypted_text = ""
+    
+    for char in text:
+        if char in reverse_key:
+            decrypted_text += reverse_key[char]
+        else:
+            decrypted_text += char
+    
+    return decrypted_text
+
+
+def display_key(key):
+    """
+    显示替换密钥表
+    
+    Args:
+        key: 替换密钥字典
+    """
+    # 构建密文字母表
+    plain_alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
+    cipher_alphabet = ''.join([key[char] for char in plain_alphabet])
+    
+    print("替换密钥表:")
+    print(f"明文字母表: {plain_alphabet}")
+    print(f"密文字母表: {cipher_alphabet}")
+    print()
+
+
+def main():
+    """主函数 - 交互式界面"""
+    print("=" * 50)
+    print("单表替换密码 (Monoalphabetic Cipher)")
+    print("=" * 50)
+    
+    # 生成密钥
+    key = generate_key()
+    display_key(key)
+    
+    while True:
+        print("\n选择操作:")
+        print("1. 加密")
+        print("2. 解密")
+        print("3. 重新生成密钥")
+        print("4. 退出")
+        
+        choice = input("请输入选择 (1-4): ").strip()
+        
+        if choice == "1":
+            text = input("明文: ")
+            result = monoalphabetic_encrypt(text, key)
+            print(f"密文: {result}")
+            
+        elif choice == "2":
+            text = input("密文: ")
+            result = monoalphabetic_decrypt(text, key)
+            print(f"明文: {result}")
+            
+        elif choice == "3":
+            key = generate_key()
+            display_key(key)
+            print("已重新生成密钥")
+            
+        elif choice == "4":
+            print("再见!")
+            break
+            
+        else:
+            print("无效选择，请重新输入!")
+
+
+if __name__ == "__main__":
+    main()
\ No newline at end of file