When a high-resistance ground fault occurs in the distribution network, the traditional route selection method is not sufficiently reliable.The difference of transient zero-sequence current under the condition of high resistance grounding while between the normal operated and fault lines is analyzed.The major difference is that the slopes of the corresponding trends of those two types of current are opposite.Therefore,a fault line selection method based on the slope of transient zero-sequence current envelope curve fitting is proposed.Firstly,the envelope curve of the transient zero-sequence current is obtained by the Newton interpolation algorithm,and then the fitting slope of each curve is calculated by the variable forgetting factor recursive least square method,and the resulting positive and negative characteristics of the slope values fitted by the envelope curves of the operating and the fault line can be utilized to construct the proposed fault line selection criterion.A large number of simulation results show that the route selection method proposed in this paper is suitable for various fault conditions.