In view of the failure of electrical maintenance personnel to effectively identify the fault problem of power supply system components in Yuxi Mining area, the fault diagnosis technology was studied in this paper. Based on the principle of fault diagnosis of power supply system components, the fault technology of diagnostic line elements, busbar elements and transformer was described. The diagnostic technology was used in the power supply system of Yuxi Mine, and the practice showed that the diagnosis technology effectively solved the problem of fault identification of mine power supply system components.