Abstract: Due to the vast access of distributed energies, the rapid growth of DC loads and the rapid development of power electronics, the DC distribution is more and more concerned, and DC power distribution system will become an important part of distribution network in the future. The protection in the DC distribution system is a core problem during rapid development of the DC distribution system, and the lucubration is urgent. Aiming at common faults such as short-circuit, ground, ring network, AC releasing into DC system and insulation decreasing fault in MV/LV DC distribution system, this paper analyzed faults characteristics and their developing process, and it proposed a power electronic protection strategy, effectively integrating the DC protection with the power electronic converters. The strategy can realize the protection and failure isolation based on the topology structure and the operation mechanism of the converter, the effective coordination between the protection action logic and control logic. And this paper expounded the applications and component of the DC active protection, analyzed the principle and method of the active protections, expounded the active ground fault protection and short-circuit fault protection, and came up with the fault mechanism and active solution method in the DC ring network and AC releasing into DC system network. At last validating through actual cases, the result shows that active protection can realize the rapid and accurate isolation of the faults in DC distribution system, and ensure the system run steadily and reliably.