The reliability of the process layer network is the key of the stability of the smart substation. In order to improve the reliability of the process layer network, a new protection method which is based on the information flow is presented. Based on the analysis of the feature of the information flow, the formation mechanism of the abnormal information flow is studied as well as the character of the fault diagnosis, and the related protection strategies are then proposed. Furthermore, based on the packet analysis of GOOSE and SV, and the information flow monitoring, the protection criterion, protection logic and threshold setting calculation are proposed. It can give alarm when the information flow is abnormal and cut off the fault. By the efforts of this paper, the communication performance of the process layer network can be improved, which will promote the stability of the smart substation.