It is difficult to analyze and verify the semantics of existing modeling methods for the objectoriented protection relay service such as UML. In this paper, according to the characteristics of Petri net, which can quantitatively analyze the security, accessibility and boundedness of system, a protection relay service model based on the Petri net is proposed. Through the UML activity diagram, the protection relay service model is initially constructed, and the activity diagram is mapped into a Petri net model. And then the Petri net is further transformed into an occurrence sequence and the structure and semantics of the occurrence sequence are verified. The branch or process in Petri net that is inconsistent with the actual procedure is searched and corrected until the occurrence sequence corresponding to the Petri net is verified. Finally, the Petri net is transformed into a protection relay service model. The case application of Petri net proves that the method can significantly improves the effectiveness of the model of protection relay services.