The design of relay protection system for mine power supply system was carried out to address the problems of poor selectivity of relay protection and frequent over-level tripping in the power supply system of Wangpo Coal Industry. The results showed that the designed relay protection system operated stably and reliably, solved the problem of overstep tripping in the power supply system, and the number of overstep tripping faults was 0 after the relay protection system was applied, reduced the labor intensity of power supply system operation and maintenance personnel and coal mining costs, and improved the utilization rate of coal mining equipment.