Abstract: DES algorithm has been facing to a lot of threat since it came out.It can be attacked easily by exhaustion attack method and chosen plaintext attack method.According to this defect of DES algorithm，this paper puts forward a kind of improved method which is based on prefix codes.By the improvement of the adjustment of the sub-key’s order，the algorithm can advance the ability to resist some attacks.With the improvement it has no effect on the efficiency，but can enhance the security greatly.

Key words: Data Encryption Standard（DES） algorithm, prefix codes, encryption, decryption, improvement

摘要： DES算法自出现以来便面对许多威胁，根据DES算法易受穷举攻击法、选择明文攻击法等方法攻击的缺陷，提出了一种新的基于前缀码的改进方案。通过改变子密钥的顺序来提高抵抗某些攻击的能力，在基本不影响DES算法效率的前提下，很好地提高了DES算法的安全性。

关键词: 数据加密标准算法, 前缀码, 加密, 解密, 改进