In order to improve the reliability of the relay protection relevant secondary circuit, a new method of the secondary circuit online monitoring and fault diagnosis which is based on multi-parameter information is presented. Based on the monitoring and analysis of the SV/GOOSE/MMS messages, the character of the abnormal information flow in process and control layer network is studied, the strategies of SV/GOOSE link breakage and data exceptions and analysis of the synchronization are then proposed. For the relay protection device, this paper puts forward a secondary circuit online state monitoring method, and sampling value exception, analog and digital monitoring, and abnormality pre-warning strategies. On the basis of gathering, analyzing and uploading of the typical alarm information when relay protection device and secondary circuit failure by the network packet analysis device or the relay protection state monitoring and fault diagnosis device, it establishes a relay protection secondary circuits monitoring and fault diagnosis system.