Abstract: A query term extension approach was used based on fuzzy set method and Wordnet for information retrieval in this paper.Wordnet was employed to find the synonyms for a query word, and the generalized Jaccard coefficient was used to calculate the similarities between the two synonyms.Then, the synonym with more similarities was selected to expand the query words for information retrieval.This approach not only kept the query word processing features simple and easy to understand for fuzzy set method, but also gave a good solution to the problem of fuzzy set method that can not accurately sort the documents.At last, the algorithm was proposed to quickly transform a Boolean expression into disjunctive normal form.The algorithm was simple, fast and solved the complicated problem for the transformation of Boolean expression into disjunctive normal form when inquires increased in the number of words.