Abstract: For the power failure of the DC power supply system in the substation, the existing solutions mostly prevent the failure from the perspective of the DC power supply system, or deal with it by putting in the standby power supply or battery. This paper puts forward an optimized scheme for line protection to deal with the DC power supply system failure of substation from the perspective of relay protection. By taking advantage of the feature that the power supply of line protection device can maintain normal power supply for a short time after power failure, connecte the DC power supply signal to a digital input of line protection, and transmitted through the optical fiber longitudinal channel with the relevant information. After comprehensively judging that one side of the DC source loses power, the other side will adjust backup protection or trip after delay. If the power supply is automatically restored in a short time, Automatic reclosing will be performed. The implementation of this scheme can be flexibly and reliably deal with the DC power failure of the substation and ensure the safe and reliable operation of the power grid.