The invention relates to a differential protection method and system for a direct-current power distribution network and an interval unit, and belongs to the technical field of power system relay protection. According to the invention, a plurality of interval units are arranged in the direct-current power distribution network and electrical quantity data acquisition is carried out in real time, sothat differential protection judgment is carried out after data interaction between adjacent interval units is carried out; when the judgment result is consistent, two adjacent interval units simultaneously execute opening operation, and the switching-off operation is executed; a protection calculation result is sent to an adjacent interval unit farther away from the fault protection area; afterthe interval unit receiving the protection calculation result continuously receives the time of the protection calculation result to reach a set value, the opening operation is executed, and the protection calculation result is transmitted to a subsequent interval unit through the interval unit according to the same method until the fault is successfully isolated; therefore, the invention providesa rapid and reliable protection method for the direct-current power distribution network, and the problem that an existing protection method is not ideal in effect in the direct-current power distribution network is solved.