With the rapid development of web services technologies, web service discovery is becoming the urgent problem to be resolved. The existing researches are not mature, and cannot cope with the requests from different fields very well. In this paper we suggest an effective and feasible approach of web service discovery based on functional semantics. By defining the web services functional semantic description model, we provide a unified approach to describe the function of web service. Based on the domain-oriented functional ontology, we propose the semantic annotation mechanism to discover web services with functional semantics. Finally we describe the web service description language FWSDL and discovery system FunWSDS.