Abstract: The traditional BM algorithm has some useless comparison,affecting the string matching speed and reducing the efficiency of intrusion detection．Therefore,this paper proposed an improved BM algorithm,applied it to the engine of network intrusion detection system．Experimental results show that,compared with BM algorithm which employs Snort detection, a network intrusion detection system constructed by improved BM algorithm can effectively reduce the false positive rate and false negative rate,and improve intrusion detection rate and time utilization．Obviously,this network intrusion detection system is very useful for enhancing the overall capacity.

Key words: Intrusion detection,Improved BM algorithm,Detection efficiency,False positive rate and false negative rate