An embodiment of the invention discloses a determination method for damping polarity supplied by a power generator excitation system in an oscillation process, and aims to solve the technical problem that the damping polarity supplied by each control system of a power generator unit in a low-frequency oscillation process is not clear caused by the fact that damping conditions supplied by different control systems of the power generator unit in the low-frequency oscillation process of the power generator unit are not analyzed independently at present while only the overall external characteristics of the power generator unit are obtained. The determination method disclosed by the embodiment comprises the steps of reading disturbance data of the power generator unit; extracting a power generator transient-state electric reactance Q-axis potential changing amount: a formula which is as shown in the description, and a power generator rotary speed changing amount: a formula which is as shown in the description, according to the disturbance data of the power generator unit; and calculating dot product values of the formulas which are as shown in the description; and determining the damping polarity supplied by the excitation system according to the dot product values.