This paper firstly analyzed the front pattern matching algorithm of intrusion detection system, and improved on the pattern matching algorithm. Having immediately analyzed Rete algorithm and aimed at its shortage, the paper introduced the FRete net algorithm on the basis of Rete net algorithm constituting an inference machine based on FRete matching algorithm, which could infer logical suspicious facts. Then the authors discussed and designed an intrusion detection system based on high-speed networks, and finally established a simula...