Abstract: Abstract: Because of the particularity and complexity of the operating environment of the low-voltage power grid in coal mine, the speed and accuracy of fault line selection by using the zero-sequence current of single-phase grounding are greatly affected. Therefore, on the basis of in-depth study of the characteristics of single-phase grounding in Small Current Neutral Grounding System, this paper puts forward the idea of combining two Small Current Neutral Grounding System for fault line selection, that is, normal operation of Isolated Neutral System when single-phase grounding, the system will operate in state of Neutral Point Grounding via High-resistance for fault line selection, after completing the fault line selection, it will return to the original state of Isolated Neutral System. A practical circuit integrating two Small Current Neutral Grounding System is given. Under the premise that the zero-sequence current of high-probability fault line is the maximum, this method can effectively improve the accuracy of fault line selection and the sensitivity of protective action by utilizing the difference between the fault and non-fault line feature which is significantly increased.