A fuzzy composition based association thesaurus with interactive query expansion for Chinese Web information retrieval is proposed. The thesaurus is well arranged by means of an organization technique, so that terms in the association thesaurus offered as suggestions could be effortless for users to decide which to add. Then, the reformulated queries accompanied with some query modification methods are submitted to perform another round of searching. Two test collections were used to construct the association thesaurus in order to see how dataset criteria affect the constructed thesaurus. Experimental results show that a homogeneous collection would get in a robust thesaurus that is useful for interactive query expansion. Besides, two weighting schemes for query modification were also examined and the results show that there are some compromises when using them. Finally, we concluded that interactive query expansion based on the fuzzy association thesaurus achieves better performance in both precision and recall rate significantly.