The invention discloses a method for grounding and selecting lines of a low-current grounding system. The method comprises the following steps of: carrying out continuous real-time sampling on zero-sequence voltage and zero-sequence current signals, obtaining sampling data and caching the sampling data; calculating the sampling data, obtaining an effective value in set time interval of the signal, and comparing the effective value with the preset threshold value; when the effective value is larger than or equal to the threshold value, determining a fault starting point, taking the fault starting point as the reference time, analyzing and calculating the sampling data which contains the reference time, and is cached in the time interval with preset length, and determining the line with single-phase grounding fault. The invention also discloses a device for grounding and selecting lines of the low-current grounding system. The invention solves the problem of selection missing and selection error because complete temporal data during the occurrence of fault is difficult to obtain by the prior art, improves the accuracy of temporal line selection and has higher credibility of detection results.