The embodiment of the invention discloses a single-phase grounding fault line selection method and device for a low-current grounding system to accurately effectively identity a single-phase fault line. The method comprises the following steps: S1, acquiring the instantaneous zero sequence current data of a single-phase grounding fault when knowing through the judgment that the low-current grounding system has the low-current grounding system; S2, intercepting part of a periodic waveform before the single-phase fault occurs and part of a periodic waveform after the single-phase fault occurs from the zero sequence current data, pre-processing the intercepted waveforms; S3, using an improved dynamic time bending algorithm to calculate the morphological distance of every two waveforms in thepre-processed waveforms; and S4, determining the single-phase grounding fault line according to the morphological distance of every two waveforms.