To solve the problems of inefficient developing, information missing and inadequate validation brought by traditional artificial constructing methods of ontology, this paper does in-depth study from the perspective of the data structure and interaction method of Web service on construction method of ontology, and analyzes the semantic information contained in Web service in detail, and proposes the basic method of construction relation model for Web service and describes mapping function between relation model and ontology. At last, we construct the ontology automatically for a series of Web services with methods above and make validation of the regression to the constructed results of the ontology. Through the analysis of verification results, we make a conclusion and outlook to the automatic construction method of ontology for Web service proposed in this paper.