The web is currently undergoing a change from a document-centered to a service-oriented environment. How to find and access the existing service in the open and distributed environments of WWW is a crucial task. The difficulty of finding suitable service is the semantic heterogeneity caused by synonyms and homonyms. Especially the customer does not know how the service is expressed and the service provider does not know what the customer wants. There are some researches about how to improve the semantic feature of service. In this paper we present the role of ontology in service discovery. Different from the existing research on applying ontology on service description, this paper focus on the application of ontology in improving the user?s initial query refinement in client end. Then, we discuss the possibility of applying ontology to domain description of service oriented system modeling.