Abstract: The security and stability control system（security control system） has many control nodes and a long control chain. If it refuses to act or malfunction due to a fault, it will cause hazard to the operation of the power grid. The fault diagnosis of the security control system is the basis for the safe and stable operation of the power system. The fault diagnosis of the existing security control system mainly relies on the technical personnel to assist in identifying the abnormal cause according to the communication message, and it is difficult to diagnose the faults of each link of the security control system in real time. To this end, the existing links and causes of faults in safety control system are analyzed, and the feature quantities of faults in safety control system are extracted. And then, a fault diagnosis model of safety control system based on deep belief network is established, and a fault diagnosis method of safety control system is proposed. Finally, the correctness of fault diagnosis method is verified by selecting the operation fault samples of the safety control system.