This paper proposes a method to utilize the correlation between query keywords in information retrieval toward extrapolating their semantic information. In accordance with the rapid development of internet and WWW (World Wide Web), it has been getting more and more hard to pinpoint the appropriate document from the huge information resource. Various search engines have been developed to retrieve the appropriate information based on the keywords, however, it is hard for the user to specify the keywords enough to pinpoint the appropriate documents. Since there often exist some semantic correlation between the keywords, this paper proposes to finding out the another keyword by utilizing their semantic correlation in order to narrow the scope of seach. Experiments were carried out to investigate the effectiveness of the proposed method and the result hinted the effectiveness of our approach as a pre-processing to narrow the scope of search for search engines.