In this paper, query expansion will be achieved by mining query information in a query log. An association will be constructed by data mining association technique. Then every incoming new query will be compared with the newly built association rule, and a new expanded query can be constructed with the original query and the newly added item. In addition, other information in the query log will also be processed to achieve query expansion. Then a performance evaluation comparison will be done among the original query, query expanded by association, and query expanded by query information. The experiment shows that the newly expanded query can produce better performance for web query searching.