In order to improve the operational safety and maintenance efficiency of secondary equipment in a power system, a smart operation and maintenance system based on situational awareness and assistant decision-making of relay protection devices is proposed. The discriminating result of protection function is given according to the comprehensive logic reasoning mechanism by analyzing the transmitted information of relay protection equipment in the substation via a system which is located in the dispatch center. Independent patrol inspection and information mutual checking mechanisms are built to quickly find and locate abnormalities among devices and circuits. Also, the protection warning processing scheme and knowledge database based on the protection information are set up to provide specific overhauling assistant decision-making in time. Then, relying on the protection operation information collection platform and the knowledge database, the collection, processing, analysis and display of historical abnormal information data of all protection devices in the region are realized. This provides a decision basis for improving the operational reliability of secondary protection equipment. Additionally, a remote operation and maintenance mode is established based on virtual connection, and direct access from the dispatch center to devices in a substation can be realized. In this way technical experts from the equipment manufacturer can help deal with field problems quickly from a remote location, and this would significantly improve the speed of field defect elimination. This work is supported by National Key Research and Development Program of China (No. 2017YFB0902605).