In order to construct a modular intelligent substation and monitor the relay protection device in real time, an online state monitoring technology for the virtual circuit of intelligent substation is proposed. Based on the whole process modularized control strategy of smart substation, this paper studies the graphical display technology of SCD files and provides integrated information such as the operating status of the device itself, the operation state of the soft press plate and the state of the logic link. In on-line condition monitoring system, entropy weight method and Grey Relational Analysis (GKA) are combined to comprehensively evaluate the fault types in the virtual circuit of intelligent substation, eliminate the problems in time, improve the work efficiency of field operations staff, and promote the development of intelligent substation. This work is supported by Science and Technology Project of State Grid Corporation of China (No. 524625160028).