When a high-resistance ground fault occurs in the distribution network, the traditional route selection method is not reliable．The difference of transient zero-sequence current under the condition of high resistance grounding is analyzed between the sound line and the fault line．It is found that the trend of the transient zero-sequence current of the sound line and the fault line is different,and the slopes of the corresponding trends of the two are opposite．Therefore,a fault line selection method based on the slope of transient zero-sequence current envelope curve fitting is proposed．First,the transient zero-sequence current is used to obtain the envelope curve by Newton interpolation algorithm,and then the fitting slope of each line is calculated by the variable forgetting factor recursive least square method,and the slope value is fitted by the envelope curve of the sound line and the fault line The positive and negative characteristics construct the line selection criterion．A large number of simulation results show that the route selection