To solve the problem of low accuracy of line selection when grounding fault occurs in a small current grounding system, a new method for single-phase grounding fault line selection in resonant grounding system is proposed. By analyzing the characteristics of zero-sequence current and zero-sequence impedance of different lines, it is found that the zero-sequence impedance of the healthy line is always capacitive, and the zero-sequence current is the pure capacitive current. But the zero-sequence current of the faulty line contains the inductive component of the arc-suppression coil in the low frequency band, and the amplitude is greater than that in the high frequency band. Firstly, the low-pass filter is used to extract the signal component of the bus zero-sequence voltage and the zero-sequence current of each feeder in the low frequency band, and the bus zero-sequence voltage is derived. Then it compares the difference between the product of the zero-sequence current and the pure capacitive current of any two lines. The one which has largest difference is the fault line. Simulations of single-phase ground fault under different working conditions have been done. The results show that the method is accurate and adaptive. This work is supported by National Natural Science Foundation of China (No. 51677060).