I ABSTRACT Network’s security has caused people’s extensive attention. Traditional safe protection technologies which adopts identification, authentication, access controlling, cryptography and so on can’t prevent the intrusion behavior which intrudes into the unauthorized computer system by utilizing computer defects of software and hardware of system, and the technique of the fire wall can not deal with the endless defects of application designing and the attacks which access the encryption channel. So it’s necessary to have a technique that can find and report the system intrusion behavior in time, namely intrusion detection. Intrusion detection which is regarded as an important technique of network protection has become a popular research direction of network security. At present, the international leading and advanced intrusion detection technique is applying data mining technique to IDS (Intrusion Detection System) in order to design an intrusion detection system that is both safe and efficient. B