In order to solve the problem of imperfect line protection in medium voltage DC distribution network，a single-pole fault protection method based on zero-mode power is proposed in this paper. Firstly，the characteristics of single-pole fault in the DC distribution network are analyzed. Fault identification is carried out by using the polarity of the transient current component，fault line selection is realized by using the magnitude of zero -mode power amplitude，and fault pole selection is implemented by using the magnitude of zero -mode voltage. Secondly，the setting criteria are given for the proposed protection method. Finally，a DC distribution network model is built in PSCAD/EMTDC to output fault data，and MATLAB is used to verify the protection method. The simulation results show that the proposed method is fast and effective，highly reliable，and has a strong ability to withstand transition resistance. It is not sensitive to data delay and has a strong anti-interference ability.