Abstract: According to the difficult judgment problem of the single phase small current grounding in the major sampling three phase center no grounding power su pply mode of the mine electric power network in China, with the references of the small current grounding line selection theory and solution of the center indirect ground ing high voltage power network, in combination of the mine power network features, the SIMULINK was applied to establish the simulation model of the mine electric po wer network. The simulation results showed that the fault compatibility current of the fault line would be more times higher than the normal line. Based on the variation fe atures of the line compatibility current and the traditional zero sequence power direction combined comprehensive fault line selection method, a double CPU fault line s election protection device combined with the electric power measuring DSP and the single chip processor was designed to solve the fault line selection problems of the mine low voltage network.