With the construction of the new power system, it is becoming increasingly difficult to obtain the steady-state component of a fault. Therefore, a power line fault analysis method based on instantaneous phase consistency using fault transient data is proposed. First, the transient data of fault current and voltage at both ends of the line are represented by a sinusoidal function, and the electrical quantity along the line is calculated. Then, according to the condition of instantaneous phase consistency of the calculated voltage at both ends of the fault point, a criterion function is constructed to determine the fault location. The general situation is that the transition impedance of the grounding fault is not pure resistance and the transition resistance of each phase of the polyphase grounding fault is not equal. Considering three kinds of ground short-circuit faults, the transient impedance parameters of the fault point are calculated using the condition of instantaneous phase consistency of voltage and current on the transition resistance. Through the analysis of simulation cases and actual field cases, and compared with other fault location methods, the fault location accuracy of the proposed method for calculating instantaneous phase consistency of voltage is significantly improved, and it has stronger applicability. From the effect of instantaneous phase consistency of voltage and current on the transition resistance, different types of fault transition impedance parameters can be effectively calculated.