Abstract: With the rapid development and application of Web service technologies, how to discover Web services based on functional semantics has already become the most urgent problem to be resolved. But in practice the existing Web service discovery methods are not mature, and cannot cope with such kind of requests very well. In this paper an effective and feasible approach to Web service discovery based on functional semantics is proposed. The Web services functional semantic description model is first defined, which provides a unified manner to semantically describe the function of Web services for service providers and customers. In order to avoid semantic heterogeneity, the domain-oriented functional ontology is built. Depending on the ontology the functional semantic annotation mechanism is proposed to further eliminate the semantic difference between the descriptive terms used by services providers and customers. Based on the above efforts the matchmaking between Web services and requests is realized. Furthermore, the Web service description language based on functional semantics is designed and a prototype system FunWSDS is established. Finally, based on the prototype system the performance of this method is evaluated by an experimental setup. The results of experiment prove that such a kind of Web service discovery method is feasible and effective.