对网络系统安全评估问题进行了研究，提出了一种评估网络系统安全的新算法。该算法基于代码分析、协议分析、脆弱性检测、认证检1测等四种网络安全缺陷发现技术，多角度查找网络漏洞，并用似然估计算法量化检测结果；同时算法中引入网络容忍度测试，以保证评估结果的可靠性，并根据该算法给出了一个完整的网络安全评估模型。关键字：网络安全，评估，脆弱性检测，漏洞检测Abstract: Through searching the problem of network security evaluation, this paperpresents an algorithm to evaluate network security. Whit fuzzy mathematic, thealgorithm disposes the primary result which is base on code analysis, protocolanalysis, vulnerability analysis and authentication detection. At last, integratethe object tolerant character, the final result was given. A whole network securitymodel base on this algorithm is presented also.Keywords: network security evaluation, vulnerability analysis, vulnerabilitydetection.