To solve the problem that the use of a large number of cable lines in the distribution line leads to a small difference between the fault line and the sound line zero-sequence current, this paper proposes a new way of fault line selection based on the phase difference between the power frequency and the characteristic frequency. On the basis of analyzing the characteristic frequency of the line, the S-transform is used to extract the amplitude information of the euploid power frequency point in the DC and characteristic frequency bands, and the range of the fault closing angle is judged by comparing the magnitudes of the two parts. The characteristic frequency of the zero-sequence current of the fault system is determined based on the principle of the maximum frequency point amplitude in the characteristic frequency band, and the characteristics of the zero sequence admittance vector are further analyzed under the power frequency and the characteristic frequency. Finally, it proposes to use that the zero-sequence admittance angle difference between the power frequency and the characteristic frequency between the fault line and the normal line is 180° to construct criterion. Based on the simulation verification of Matlab, this line selection method has a good line selection effect. This work is supported by National Natural Science Foundation of China (No. 51607106), Key Projects of the Science and Technology Research Program of the Hubei Provincial Education Department (No. Z2017037), and Research Fund for Excellent Dissertation of China Three Gorges University.