The invention discloses a dispatching side transformer substation small-current single-phase grounding automatic line-selection method. The method comprises the following steps: judging whether one ofthe following three conditions is satisfied: zero-sequence voltage 3U0 is greater than 15V, phase voltage (U1, U2) is greater than 7kV and U3 is less than 5kV, or a bus is in grounding action and thesustained computing period is equal to 2; if one of the three conditions is satisfied, storing bus voltage, recording line load and zero sequence current of the line under each of a running state anda fault state; performing running line comparison satisfaction: enabling the difference obtained by subtracting IN0 initialization from IN0 fault to be unequal to 0, and the MAX(IN0 fault) and MAX(IN0 fault-IN0 initialization), or MAX(2*IN0 fault-IN0 initialization), outputting a line ID, and giving an alarm instruction, ending the operation. The method disclosed by the invention has the advantages that the ground fault line can be quickly and accurately determined when the system is in single-phase grounding, the accident processing efficiency is improved, the power grid supply stability isimproved; the power supply reliability of the electric user is guaranteed, and the comprehensive economic loss caused by power failure or unqualified electric energy quality is reduced.