In view of the cable grounding short circuit fault often caused by mal-condition in coal mine, the analysis says the timely discovery of the fault point is of great importance to coal mine power supply security, then traveling-wave based fault location which has been widely used in large power system is introduced into the underground circuit fault positioning, the single-ended fault location algorithm is improved according to the actual situation and feature information of the fault travelling wave is extracted using wavelet transform, Through the calculation of modulus maxima of wavelet coefficient to confirm the breakpoint of the signal. Simulation examples show that this method can realize relatively accurate position of the underground power grid fault.