Web Services promote the specification-based cooperation and collaboration among distributed applications in an open environment. To ensure the quality of the services that are published, bound, invoked and integrated at runtime, test cases have to be automatically generated and testing executed, monitored and analyzed at runtime. This paper presents the research to generate Web Services test cases automatically based on the Web Services specification language WSDL (Web Services Description Language), which carries the basic information of a service including its interface operations and the data transmitted. The WSDL file is first parsed and transformed into the structured DOM tree. Then, test cases are generated from two perspectives: test data generation and test operation generation. Test data are generated by analyzing the message data types according to standard XML schema syntax, Operation flows are generated based on the operation dependency analysis. Three types of dependencies are defined: input dependency, output dependency, and input/output dependency. Finally, the generated test cases are documented in XML-based test files called Service Test Specification.