Abstract: In the development phase of Web services, the services located in different locations and provided by different organizations must be composed together in order to satisfy specific business requirements. The reliability must be ensured for composite services first. The reliability of composite services is the most important QoS(Quality of Service)which can determine the popularity of the services. The reliability of composite services is affected by the structure of services and by the composite conditions. So, the traditional models to predict the reliability are inapplicable to Web services. In this paper, to improve the accuracy of reliability prediction, a reliability prediction model for composite service was presented based on control-structure. Lastly, a case study was designed to support our reliability model. The experimental results show that our model can obtain better reliability prediction accuracy.

Key words: Control-structure, Composite condition, Reliability prediction, Web service