In view of the problems such as rapid rise and large amplitude of fault current and difficultly distinguishing the faults in and out of the region when threeterminal annular DC distribution network generates faults, a protection strategy based on current information is proposed. The main protection proposes to firstly block the convertor in fault transient state, stop the transmission of each end of power supply and distinguish the faults in and out of the region based on the fault current direction in the line at this time. In order to make up the defect of resistance of the main protection in the case of blocking fault of the convertor, the backup protection based on abruptly changing rate polarity of fault current is provided, and the protection strategy of threeterminal annular DC distribution network is constituted. In PSCAD/EMTDC environment, threeterminal annular DC distribution network is built, and the simulation is carried out under the condition of interelectrode shortcircuit fault. Simulation results show that the main protection system in protection strategy can effectively judge the fault line, and the circuit breakers of other lines will not be misused. When the main protection is blocked, the backup protection is started to identify the faults in and out of the region and ensure the safe operation of the distribution network so as to verify the effectiveness of the proposed protection strategy.