Abstract: Sentence similarity computing plays an important role in machine question-answering systems，machine-translation systems，text categorization systems，etc.Aiming at a sentence similarity model based on key words，an improved method is put forward，including the extraction of keywords，and the induction of synonyms in sentence similarity definition.And on this basis，a question answer system based on FAQ（Frequently Asked Question） is implemented.This system involves automatically searching for candidate question set，computing sentence similarity and returning the answer to the user.This system can also automatically update and maintain FAQ.Experiments’ result shows that the new method has more accuracy than the others in matching questions of question answering system.

Key words: natural language processing, sentence similarity, Frequently Asked Question, question answer

摘要： 计算句子的相似度在机器问答、机器翻译、文本分类等系统中有着非常重要的作用。该文对基于相同关键词的句子相似模型作了进一步的改进，包括关键词抽取，以及在句子相似度的定义中引入同义词以及近义词的情形。并以此为基础，实现了一个基于常问问题集的中文自动问答系统，对用户以自然语言输入的问题，该系统能够自动地在FAQ（Frequently-Asked Question）库中寻找候选问题集，通过计算句子相似度，将匹配的答案返回给用户。该系统还能够自动地更新和维护FAQ库。实验结果表明，这种新方法在问答系统中匹配问句时比其他方法具有较高的准确率。

关键词: 自然语言处理, 句子相似度, 常问问题集, 问答系统