The evolution of Grid technologies has brought to the world a loosely coupled environment that enables flexible integration among heterogeneous systems. On building a service-oriented architecture for Grid systems, more and more research is focused on service composition, in which workflow and simulation techniques have shown great potential. Simulation of services? interaction is important since the services eco-system is unstable and in continuous evolution. However, there is a lack in the research of services? simulation, especially models and methods for simulating interactions between composite services. In this paper a workflow simulation method based on interactive events is proposed to fulfill this requirement. By introducing an event submodel in the workflow meta-model, the event interaction pattern is achieved from both the build-time and run-time perspectives. With an example simulated in the prototype system developed according to our method, the advantages of our method in model verification and QoS evaluation for service composition are also highlighted.