Abstract: With the continuous expansion of the DC power supply system for rail transit, problems such as misoperation, refusal to operate, and insufficient fault removal efficiency of protection devices have become increasingly prominent, seriously threatening the continuity of power supply and driving safety. Therefore, this article focuses on the DC power supply system of rail transit, deeply studies the selection and configuration of relay protection devices, analyzes the types of faults and protection requirements of the DC power supply system, and then determines the selection principles and configuration design. The article combines a practical case of a subway line to verify the advantages of scientific selection and configuration, which can shorten the average fault removal time of the system, reduce the power supply recovery time in non fault areas, and provide theoretical basis and practical reference for ensuring the safe and stable operation of the rail transit power supply system.