In view of the problem that the protective device of aircraft ring distribution system can’t effectively protect the power distribution system, the directional locking longitudinal protection is introduced into the power supply system of the aircraft ring-network. Based on the Matlab software, the aircraft ring-network power supply system is modeled and the fault is simulated. The directional locking longitudinal protection method is proposed based on fault characteristics. The simulation results show that the protection method can automatically isolate the faults of the ring-network, ensuring the safety of the power distribution system, and the reliability of the power distribution effectively.