Abstract To meet the needs of the promotion of “equipment ownership” and the implementation of a centralized monitoring mode in substations, a technical scheme of unified monitoring, online operation, and maintenance for secondary equipment in substations is proposed, considering the monitoring, operation, and maintenance requirements of secondary equipment such as protection devices and automation devices. A secondary equipment monitoring real-time gateway is arranged in Security Zone I. The comprehensive operation status data of various secondary equipment is collected, analyzed, processed, diagnosed, and applied through various apps, to realize heterogeneous access, on-demand deployment, and flexible expansion. The master station is designed with functions such as human-machine interaction and remote analysis for secondary device monitoring and operation. GSP, MQTT, and other service-oriented and message mechanism communication protocols are adopted between the substation and the master station to meet the diversified and easily expandable information exchange requirements. Through the factory test, it is verified that the scheme can realize the panoramic perception of the operation state of the secondary system and effectively improve the ability of abnormality diagnosis and processing.