In order to improve the safety of mine production, Xiangsheng Mine made an anti-overstep modification to the power supply system of the mine. The anti-crossing trip system were introduced, and the working mode of the KJ171Mine power supply anti-crossing trip monitoring system was analyzed. Through the application in Xiangsheng Mine, it can be found that the system had selectivity, rapidity (zero time limit) and reliability in anti-step-over tripping, which guaranteed the safe mining.