With the evolution of grid technologies and the application of service-oriented architecture (SOA), more and more enterprises are integrated and collaborated with each other in a loosely coupled environment. A business process in that environment, i.e., the service-oriented business process (SOBP), shows highly flexibility for its free selection and composition of different services. The performance of the business process usually has to be evaluated and predicted before its being implemented. And it has special features since it includes both business-level and IT-level attributes. However, the existing modeling and performance evaluation methods of business process are mainly concentrated on business-level performance. And the researches on service selection and composition are usually limited to the IT-level metrics. An extended activity-network-based SOBP Model, its three-level performance metrics, and the corresponding calculation algorithm are proposed to fulfill these requirements. The advantages of our method in SOBP modeling and performance evaluation are highlighted also.