The universal search engine, which is widely used now, has significantly improved the efficiency of retrieving information. According to CNNIC (China Internet Network Information Center) 26th Internet survey, the search takes up 76.30% for absolute advantage as a major way for users to obtain information from the Internet. Among almost all the surveys of using on the Internet in the world, search engine is second only to e-mail service. But with the growth of a wide range of information, these universal search engines can not meet people's needs either in retrieval precision or in retrieval efficiency when retrieving information on a subject or topic. That's because as long as the user enters the same keywords, the feedbacks of universal search engine are just the same. Universal search engine does not take the differences in interests and needs between different users, which often exist, into account. For example, dentists and ceramics enthusiasts would hold different concerns about the term "ceramic". In order to be more rapid, accurate and efficient in retrieving information on particular subject or theme, it is essential to develop information retrieval systems on specific areas, that is, the domain-specific search engine.