Abstract: For the difficulties that affect the quality of keywords extraction,such as the phenomenon of polysemy,synonyms as well as the accurate and comprehensive expression of the subjects in the text,a method named KESELC based on the semantics of keyword extraction was proposed．By calculating semantic similarity and semantic relevancy based on the tongyici cilin and statistical information,then the concept of semantic expansion and its calculation method were proposed.By combining semantic expansion with lexical chain,it made the text processing in terms of preprocess,polysemy disambiguation,synonym mergence,the construction of lexical chains,feature selection and improvement of weights computation．The extracted keywords not only avoid a redundant expression,but also cover the subjects of the article accurately and comprehensively．The experimental results show that the method of keyword extraction based on KESELC has better performance than the ones based on TFIDF and Lexical chain, and has a certain practical value.

Key words: Tongyici cilin,Semantic expansion,Lexical chain,Keyword extraction,Semantic analysis