Power system design, the load statistics and calculation by reasonable methods, can provide an important basis for the selection of electrical equipment, transmission lines and relay protection device of coal mine power supply system, effectively support the analysis of mine power supply system, help enterprises to do a good job in construction planning, and avoid the phenomenon of repeated investment and waste. This paper takes the design of power supply system of Wangwa Coal Mine in Wangwa Coal Industry Company as an example, analyzes the content and common problems in mine power supply design from the aspects of basic data collection, calculation and analysis, the determination of the main connection mode of mine power supply and substation, equipment selection and cable selection, so as to provide experience for other engineering design.