Abstract: With the development of DC conversion technologies and the practical need for DC power supply, DC distribution systems attracts more and more attentions around the world. Furthermore, the national criterion GB/T 35727—2017 of China for standard voltages of medium and low voltage DC distribution system is published recently, which is very important for the development of DC distribution system since voltage levels and series are the key points for power system research and design. The background of this criterion is introduced in this paper, followed with the main parts of medium-level nominal voltages, low-level nominal voltages and the corresponding permitted voltage deviations with main factors considered. Finally,this paper puts forward a power supply mode analysis method of DC distribution system based on load distance, which links voltage level, allowable deviation, line parameters, transmission capacity, etc. to provide support for the analysis and design of power supply mode of DC distribution system.