There is limited research on fault line selection methods for low-voltage DC microgrid lines. Thus this paper proposes a fault line selection method based on the Pearson correlation coefficient and generalized S transform. First, the general composition of a low-voltage DC microgrid is introduced. Then the fault characteristics of unipolar and inter-pole faults of low-voltage DC microgrids are studied, and a line selection method is proposed. The Pearson correlation coefficient calculation is performed on the current difference between the first and last ends of two polarities of each line to determine the fault line. Then it does generalized S transform on the current at the head of the positive and negative lines of the selected fault line, and the ratio of energy sum is calculated to identify fault polarity or inter-pole fault. Finally, a low-voltage DC microgrid model is built in PSCAD/EMTDC to output the current data of each line, and then Matlab is used to simulate the data. The results show that the line selection method proposed is direct and effective, and the ability to withstand transition resistance is strong.