Abstract: Pattern matching algorithm is an important algorithm，used by most of Intrusion Detection System.On the base of analyzing BM algorithm and other algorithms，a new improved pattern matching algorithm—BMI algorithm is presented.The algorithm makes reference to the idea of BM algorithm and makes use of singleness and combination of the last character and next character of string，increasing the probability of maximum displacement effectively.Test results show that the algorithm can effectively improve the efficiency of the matching process.

Key words: intrusion detection, pattern matching, Boyer-Moore（BM） algorithm, string searching

摘要： 模式匹配算法是入侵检测系统中使用较多的一种重要算法。在分析了BM算法以及相关算法的基础上，提出了一种新的改进算法——BMI算法。该算法借鉴了BM算法的思想，并利用了下一字符和末字符的单一性和组合性，有效地提高了最大位移出现的概率。实验测试结果表明该算法能够有效提高匹配过程的效率。

关键词: 入侵检测, 模式匹配, Boyer-Moore（BM）算法, 字符串检索