The invention discloses a method for identifying an excitation surge current in the technical field of excitation surge currents, and aims to solve the technical problem of error operation of differential protection of a transformer caused by low harmonic content of the excitation surge current in the prior art. The method comprises the steps of calculating instantaneous excitation inductance values of sampling points in real time after differential protection is started; comparing the differences between the instantaneous excitation inductance values and a set excitation inductance threshold,thereby judging the states of the current points of the transformer; continuously judging the number of the unsaturated-state sampling points of the transformer in a cycle, and judging whether the differential protection is locked or not; and after each sampling point data window is identified, moving one sampling point backwards, repeating the steps, and cyclically judging the excitation surge current. According to the method, the excitation surge current is identified by scanning the instantaneous excitation inductance value trajectory of the differential protection; the method is simple and practical, the program is easy to realize, and the method has wide applicability; and meanwhile, the error operation of the differential protection of the transformer caused by low harmonic contentof the excitation surge current is effectively avoided, and the reliability of the differential protection is improved.