Single-phase grounding fault line selection in ungrounded or high-resistance grounded systems faces challenges such as weak fault signatures and susceptibility to transition resistance. 220 Hz is selected as the characteristic frequency for current injection and a PSCAD/EMTDC simulation model of a distribution network is established to analyze the amplitude characteristics of characteristic frequency signals on each line. Using the envelopes of the injected characteristic frequency zero-sequence currents, a linear correlation-based line selection method is proposed, and the grounding fault line selection method is designed. Simulations of single-phase grounding faults with varying fault locations and transition resistances were conducted, and the proposed method was applied for fault line selection. The results confirm that this method remains effective to large transition resistance effects and achieves accurate fault line selection.