Abstract: Aiming at the difficulty in selecting the fault lines when the high resistance grounding fault occurs in the flexible grounding system of a distribution network, a method of the fault line selection is proposed using the characteristics of the phase change of the zero-sequence current. The characteristics of the phase differences of the zero-sequence current between each line and the neutral point are analyzed in detail when a single-phase grounding fault occurs. Before the parallel small resistance is put into use, the phase difference of the zero-sequence current between each line and the neutral point is 180°. After the parallel small resistance is put in, the phase difference of the zero-sequence current between the sound line and the neutral point is about 90°, while the phase difference of the zero-sequence current between the fault line and the neutral point is about 180°. The cross-correlation coefficient reflects the phase differences of the zero-sequence current between each line and the neutral point, and the differential criterion of the cross-correlation coefficient is constructed to further enhance the differences in the fault characteristics. At the same time, the neutral zero-sequence current is used to calculate the zero-sequence current of a sound line with a weak amplitude, effectively reducing the risks of misjudgment by the fault line selection devices due to the failure of accurately collecting the zero-sequence CT. Simulation results of the PSCAD show that this method is suitable for the ground faults with a transition resistance less than 3000 ohms. It has rather high reliability under the extreme conditions such as a zero-sequence CT reverse connection and a strong noise interference.