The power supply structure and load situation of the DC system of the secondary equipment of the 110 kV substation in the Xiegou mine were studied. The hidden safety hazards in the DC system of the substation were analyzed. The intelligent insulation monitoring device realizes real-time online monitoring of the DC feed-out line, solved the problems of difficult search and handle, and large scope of power loss in the substation DC system, and ensured the safe and stable operation of the substation.