Abstract: To solve the problem of inaccurate fault phase identification in single-phase grounding faults of low current grounding systems, the variation of three-phase current in the fault line was analyzed, and a transient criterion for determining the fault phase was derived based on the characteristics of the transient current waveform. At the same time, the characteristics of steady-state voltage were analyzed, and the fault phase was determined based on the effective value of steady-state voltage and the angle between them. The adaptive method combining transient state criterion can improve the accuracy and reliability of fault phase selection, effectively solving the shortcomings in existing technology.