With the development of DC power transmission technology

it is possible to develop a multi-level DC distribution system. This paper firstly analyzes the basic principles and main constraints to design DC distribution network voltage class series. Based on the analysis of DC power distribution capacity with each voltage level

a set of DC distribution network voltage class series is proposed in which high voltage

medium voltage

low voltage and ultra-low voltage cooperate with each other. The related equipment manufacturing level and power grid topology optimization should be taken into account in voltage class series based on load demand. Finally

the economy of multi-level DC distribution is briefly analyzed. This work is supported by National Natural Science Foundation of China (No. 51277083).