Abstract: In view of problem of traditional leakage detection method of DC power supply system in overhead line system that it has detection dead zone and big voltage deviation between bus and ground, a new kind of leakage detection method based on balancing bridge method and switching bridge method was proposed. Detection principle of the method was analyzed and computational model of balancing resistors and switching resistors were established from the perspective of lowering voltage deviation between bus and ground. The Simulink simulation results show that the new method can reduce voltage deviation between bus and ground, and improve stability of the power system.