The rapidly growing number and complexity of web services available on the Web raise a novel and challenging problem: utilizing semantics to organize web services for more effective services searching. Traditional UDDI is insufficient in this context, since the underlying semantics of web services are not exploited enough. Also, the user requirements are not described explicitly and consistently. Considering this situation, we construct a SAM-based service model for web services management, SAM-WS, and propose an approach for users to explicitly describe their QoS requirements using QoS ontology. Experimental results show the effectiveness by comparison of our approach and traditional keyword search.