To improve the level of limitation of high resistance single-phase grounding line selection in resonant grounding systems, a single-phase grounding line selection approach based on correlation detection is proposed. The compensation current of an arc suppression coil is modulated with a low-frequency square wave. The signal characteristics of fault and healthy lines after modulation are analyzed. The zero-sequence current of each line divided by the amplitude of zero sequence voltage enveloping is used for demodulation and correlation detection. A single-phase grounding line selection criterion based on a cross-correlation function is constructed and the influence of the selection of low-frequency modulated square wave frequency on line selection effect is analyzed and discussed. Simulation and experiments are carried out, the results of which show that it can accurately select the single-phase grounding line with a large high grounding resistance. This work is supported by the National Natural Science Foundation of China (No. U1766208).