Service Oriented Computing (SOC) is changing the way of developing software systems. Each web service has a specific purpose to serve, so it can not satisfy users’ request. In this paper, we propose a Web services composition method based on OWL ontology, and design an automatic system model for services discovery and composition. This method uses domain ontology and WordNet to calculate matching between input and output parameters and uses Category ontology to solve the problem of semantic heterogeneity in web service description. We use services with single input and single output and cost as QoS criteria. This method can enhance the efficiency and accuracy of service composition, and the experiments are used to validate and analyze the proposed system.