In the paper, firstly, the insulation aging and insulation cut or crack fault models of DC feeder cable were established; then according to the characteristics of electrical and loads of DC feeder cable, the Rail-Voltage law and different DC current law were purposed in the orbital theory, and the feasibility of purposed law were discussed from engineering view. The results of analysis show that the Rail-Voltage law could not be carried out in real project, because there were lots of interferences and could not be separated; and the different DC current law meets the real projection request and could be carried out. Lastly, simulation tests were done to investigate the effectiveness of different DC current law to detect the cable faults in the Laboratory. The results of experiment show that the different DC current law had great limitations on detecting insulation cut or crack fault of DC feeder cable, and the effectiveness was impacted by the environment especially soil moisture. Another law should be found to living detect the insulation cut or crack fault of EPR DC cable.