Abstract: According to the operation character of the coal mine power supply system in overcompensation state, this article introduces the method to locate the substation with single-phase grounding fault circuit by analyzing the decaying DC component of upper substation and lower substation. When single-phase grounding fault happens in coal mine 6 kV grid, the DC component of fault circuit is the largest at the beginning and the DC component of each circuit begins to fluctuate after one wave cycle, Non-fault circuit DC component decays to almost zero, but Non- fault line still exists a large DC component. This method can be used to locate the substation with fault circuit, narrow the area of the fault circuit that need to locate, which reduces the calculation and improves the accuracy of common line selection criterion.