Web applications have become complex and crucial in many fields. In order to assure their quality, a high demand for systematic methodologies of Web application testing is emerging. In this paper, a methodology of Model-Driven Testing (MDT) for Web application is presented. Model is the core of this method. Web application model is built to describe the system under testing. Test case models are generated based-on the web application model. Test deployment model and test control model are designed to describe the environment and process of test execution. The test engine executes test cases based-on the test deployment and control model automatically. After that, testing results are reflected to test case models. A framework is designed for supporting this methodology. In order to get better extensibility and flexibility, it is loose-coupled by a modeler and a tester. The modeler enables developers to design meta-models, and is responsible for creating, visualizing and saving models. ...