Abstract: A service class can be formed by Web services with the same function from an abstract operation. Some operations for the service class are presented to reflect its self-adaptation. On the basis of the service class, Web service discovery and composition algorithms are given. In Web service discovery process, a projective operation is proposed and a selection algorithm is provided to choose the optimal Web services and in Web service composition process, some service composition operations are given. The Web service discovery and composition efficiency is improved based on service classes. Finally, the effectiveness of the proposed methods is illustrated by the service composition for travel planning.