Abstract: Short-circuit faults in power systems can be regarded as the superposition of normal load states and fault transient processes. This paper proposes a single-terminal distance measurement method based on voltage phase mutation: when a line fault occurs, the voltage phase at the fault point will undergo a significant jump, and the phase difference before and after the fault is π. By collecting voltage and current data at the measurement end and combining the line model to calculate the phase distribution along the line, the fault location can be determined by locating the phase mutation point. This method only requires single-terminal measurement, has a simple principle, and has more practical advantages compared with traditional impedance methods and traveling wave methods.