The invention discloses a DC line fault protection method based on a current converter injection characteristic signal. The method comprises the following steps: step 1: establishing a full-bridge modular multilevel current converter; step 2: when a DC line fault occurs, starting a characteristic signal injection strategy to inject the characteristic signal after a fault clearing strategy is started for a certain time, wherein the characteristic signal injection strategy can generate an identifiable characteristic signal in the line; and step 3, after the characteristic signal injection strategy is started, judging whether the fault exists through wavefront refraction. By adoption of the DC line fault protection method disclosed by the invention, permanent faults and transient faults can be quickly distinguished, when the fault is determined as the permanent fault, the fault distance can be accurately judged, and a function of fast restart of a fast arc-extinguishing fault and the non-start of the permanent fault is achieved; and by adoption of the DC line fault protection method disclosed by the invention, adaptive restart is achieved on a DC overhead line, adaptive identificationof the fault nature and the fast restart of the fast arc-extinguishing fault are achieved, the safe and reliable operation of a DC system is ensured, the power outage loss is reduced, and the directbenefit and the indirect benefit are very significant.