Abstract: The paper introduced principle of grounding fault of low-voltage IT grounding system in underground mine for the first time, and pointed out it is meaningless of a requirement in GB 50070-2009 Design Code for Electric Power in Mine that fault current should not be greater than 5 A when fault with negligible impendance occurred between phase conductor and exposed conductive part of power distribution system for the first time. It also calculated electric shock voltage and current when single-phase grounding fault occurred in IT system and TN system respectively, and got conclusion that the current of direct electric shock in IT system is the same as the one in TN system, and IT system is better than TN system under condition of indirect electric shock.