Aiming at this painful point that the DC circuit of the substation cannot be monitored in real time for a long time, this paper proposes a solution to add a loop current monitoring module to the DC circuit to pre-alarm abnormal loops, and integrate it into the relay protection device. Finally, the correctness of the principle and the feasibility of the scheme were verified through targeted experiments. This solution is conducive to timely and accurate detection of defects such as increased contact resistance of the switch circuit, and can effectively avoid major economic losses caused by switch refusal.