Abstract: In the flexible DC distribution system, the DC pole-to-pole short-circuit fault makes the converters of the whole network quickly locked, which is faster than the action time of the DC circuit breaker, leading to the system outage and greatly reducing the reliability of the system. Therefore, this paper proposes a line protection method based on incipient fault section location for DC cable incipient short-circuit faults. Through the active injection of the local converter, the attenuation of the line impedance to the injected signal is weakened; the characteristics of incipient faults are displayed; the accurate identification and section location of incipient short-circuit faults are realized; and the problem of system power loss caused by short-circuit faults is solved. To avoid frequent injection, an injection starting criterion based on differential current measurement is proposed. The simulation results with PSCAD/EMTDC show that this method can accurately identify and locate the incipient fault section and promptly isolate the fault branch, and has a small impact on the system operation. It has a certain anti-noise ability, and guarantees the continuous and safe operation of the flexible DC distribution system.