Abstract: The paper analyzed fault components at the electric leakage moment of isolated neutral power supply system and power supply network connected to earth through an arc suppression coil, and got electrical characteristics of fault point. It also analyzed distribution of zero-sequence current of mine multi-level power supply network and got following collusions: (1) When electric leakage fault happens in isolated neutral power supply system, leakage current of the grounding line is the maximum in the whole power supply system, and zero-sequence current of the grounding line is bigger than the ones of the superior lines. (2) When electric leakage fault happens in power supply system connected to earth through an arc suppression coil, zero-sequence current value of the grounding line may be similar to the ones of other lines in the whole power supply system, but active component of the zero-sequence current of the grounding line is far more than the ones of non-grounding lines and the superior lines. Finally, it introduced several detecting principle of electric leakage protection of isolated neutral power supply system, and emphatically analyzed an electric leakage protection scheme of power supply system connected to earth through an arc suppression coil which is easily implemented in microcomputer protection, namely line selection method based on zero-sequence active power of lines.