In this paper, the grounding line selection technology is applied to the field. Under a substation model, the SL-0l grounding line selection device is used for small current system, and multiple tests are carried out in the field, and the corresponding waveform analysis is carried out. In this paper, the principle of small current system single-phase ground fault line selection based on transient traveling wave is studied, and the influence of neutral grounding method on traveling wave line selection method is analyzed. The corresponding device hardware and software algorithm is designed to solve the high frequency problem. Field test results and waveform analysis show that under the existing technical conditions, it is feasible to use high-speed sampling technology and wavelet algorithm for traveling wave selection. SL-0l traveling wave line selection device can meet the needs of the site.