Abstract: There is a spare relay in the circuit design of the operating box of the relay protection device. Long-term live in actual operation may cause the relay resistance to overheat and damage the operating box circuit, which will affect the circuit function of the device and even cause fire. In this paper, through the simulation model analysis of temperature and resistance (power), current and time, the access loop of the standby relay is proposed to optimize and the scheme is given, and the predetermined effect is achieved. This method can effectively eliminate hidden dangers and ensure the normal operation of the relay protection device, which has guiding significance for the loop design of the operation box.