An arc suppression coil-grounded system with medium resistance increases the availability of information for fault line selection and section location. This paper proposes a novel method of fault line selection and section location based on the increment coefficient of power frequency. It analyses the input time and the cutoff time of medium resistance when the system fails and explains the fault characteristics and differences of power frequency information of zero sequence current between the input and the cutoff of medium resistance. Research shows that the zero-sequence current component of a fault line increases rapidly and the zero-sequence current component of a healthy line decreases. The zero sequence current component of a fault section upstream increases rapidly and downstream it decreases. Aiming at the difference, the half cycle integral values of zero sequence current component are calculated as an increment coefficient of power frequency K. Based on the comparison of the K value of the fault line and a healthy line, and the K value between upstream and downstream in the fault section, the method achieves fault line selection and section location. A hybrid cable-overhead line system simulation model is established in Matlab/Simulink, and results verify the effectiveness of the fault line selection and location method. This work is supported by the National Natural Science Foundation of China (No. 52077120).