When a short circuit or grounding fault occurs in a DC distribution network, its fault characteristics are complex, and a fast and reliable fault protection method is the key to ensuring the safe operation of the DC distribution network. A fast and reliable fault protection method is an important guarantee for the safe operation of DC distribution networks. A DC distribution network pilot protection method is proposed based on the cosine similarity of the transient voltage of the current-limiting reactor. Firstly, the differences in the voltage characteristics of current-limiting reactors at both ends of the DC line are analyzed when a single line-to-ground or line-to-line faults occur inside and outside the DC distribution network, and according to the principle of cosine similarity, a fault discrimination method based on the cosine similarity of transient voltages of current-limiting reactors is proposed for the fast identification of internal/external DC fault. Then, the voltage surge ratio between the positive and negative poles of the current-limiting reactor is used to identify the type and polarity of DC faults, based on which corresponding protective measures are taken. Finally, a simulation model of a multi-terminal radiated DC distribution network is built using PSCAD/EMTDC simulation software. The effectiveness of the proposed protection method is verified. The simulation results show that the method has a certain degree of resistance to fault resistance and can better meet the rapidity and selectivity requirements of DC distribution network protection.