Nowadays there are more and more requests from life and business. Those requests can be realized by composing the existed services. There are multiple models can specify services. To compose the services which are specified by different models, it’s necessary to unify those models. Formal grammar is used as unified model. Görlach presents a concept to transform existing service composition models to a unified model. Based on the work, the control flow based language, BPEL is focused on in this thesis. This work implements the transformation of BPEL to formal grammar. The architecture of implementation is introduced. To test and verify the implementation test cases are represented.