Abstract: The reliability and performance of individual Web service are related to the users locations, because service interaction behaviors can be easily influenced by the unpredictable Internet environment. By coordinating service interactions between different individual Web services, service composition is able to carry out much more complex functions. As a result, service composition is also greatly impacted by the Internet environment. However, current modeling methods of service composition focus on composition itself without the impact of the Internet environment. It causes great deviation between actual situation and evaluation results from such modeling methods. This paper introduces a Web services interaction behaviors-environment model based on generalized stochastic Petri nets. The modeling method takes into considerations not only the situations of individual Web services but also the factors of the Internet environment. The model is used to evaluate the reliability and performance of service compositions and predicate service interaction behaviors. Qualitative and quantitative analysis can also be performed by this modeling method, so as to give some guidance about optimization approaches to service composition plan and evaluate the impact of the Internet environment on service interaction behaviors. Finally, a case study is provided with full evaluations of the reliability, performance of service composition, and service interaction behavior properties.