Abstract: In view of low reliability of leakage protection device of coal mine low-voltage power grid based on line selection principle of zero-sequence power direction, a hardware and software design scheme of mine-used low-voltage leakage protection device was given. Fault line selection is realized according to differences of phase difference between zero-sequence current and zero-sequence voltage in non-fault branch and fault branch when single-phase grounding fault occurs in zero-sequence reactor grounding system with parallel resistance. The simulation and test results show that the device is not affected by zero sequence reactor compensation in power grid, and can operate quickly and reliably when single-phase grounding fault occurs.