The invention discloses a field measurement method for reactive current compensation ratio of a power generator excitation system, and belongs to the technical field of power generation. The field measurement method for the reactive current compensation ratio of the power generator excitation system comprises the steps of measuring a voltage of a first machine end of a power generator when reactive current compensation is not added; adding the reactive current compensation into the power generator, and simultaneously measuring a voltage and a reactive power of a second machine end of the powergenerator; calculating to obtain reactance of the reactive current compensation according to the voltage of the first machine end and the voltage and the reactive power of the second machine end; andcalculating to obtain the reactive current compensation ratio according to the reactance of the reactive current compensation and a reactance per unit value of the power generator. By testing the voltages of the machine ends before and after reactive current compensation of the power generator and the reactive power after compensation of the power generator, simple calculation can be performed toobtain the reactive current compensation ratio of the power generator, the operation method is safe and simple, and large-size interconnection power system can be effectively applied to a complicatedenvironment.