Web services have been increasingly used to integrate and build business applications over the Internet in the recent years. Once a Web service is published and deployed, other applications can discover and invoke it. A component Web service usually provides clients with single and simple functionality, but complex Web-based applications and business communities often involve different kinds and numbers of Web services to achieve their objectives. This puts forward to a challenge: how to automatically compose component Web services to form a new composite Web service? In this paper we study the issue of composing Web services with combination of Ontology, Web services and agent technology. We present a goal-driven and ontology-based architecture in which (1) user?s goal is decomposed to subgoals; (2) the information in the goal and Web services are annotated with domain specific ontology; (3) AI technology and theory of reasoning about action are used to compose Web services. We also present a composing algorithm to show an application.