The traditional redundancy mechanism cannot be realized when there are problems of zero recovery time and zero data frame loss in the communication system of an intelligent substation. This paper takes the reliability of a communication network of intelligent substations as the research object, and proposes a system model combining a parallel redundancy protocol and a high availability seamless ring network protocol. A model is established by using a redundancy protocol in the station control layer and the ring network protocol in the process layer. The reliability is evaluated by a reliability block diagram and the success flow method. The effectiveness of the method is verified by an example. The results show that the method can effectively improve the reliability of the communication network and provide a reference for the development of an intelligent substation. This work is supported by the Science and Technology Project of State Grid Corporation of China (No. 5216A0180003) and the Science and Technology Project of State Grid Hunan Electric Power Co., Ltd. (No. 5216A5180016).