In mine power systems, false operation and failure operation of relays in parallel supply lines often take place when single phase grounding fault occurs. A novel method based on phase-to-phase current difference is proposed as line selection criterion in this paper. The method builds on that the phase-to-phase current difference based on fault phase in fault line is equal to the grounding fault current while the phase-to-phase current difference based on fault phase in sound lines is equal to zero. Thus the fault line was selected by the biggest phase-to-phase current difference of the lines. The simulation results using PSCAD and experiment results show that the method has a high accuracy and a great ability of anti-disturbance. It is quite effective when single-phase-to-earth fault occurs in one of the parallel supply lines. It also applies to any distribution system with different grounding patterns and won’t be affected by the value of grounding resistance or the degree of fault phase.