The invention provides an oscillation restraining method and device for a train traction system. The oscillation restraining method comprises the steps that the distortion degree of the input tractionvoltage, the distortion degree of the supporting capacitor side voltage and the distortion degree of the input current of a current transformer are calculated; according to the distortion degree of the input traction voltage, the distortion degree of the supporting capacitor side voltage and the distortion degree of the input current, a first traction brake level signal is corrected, and thus a second traction brake level signal is obtained; and according to the second traction brake level signal, the output torque of a traction motor is adjusted. According to the oscillation restraining method and device for the train traction system, characteristic contents corresponding to the input traction net voltage, the supporting capacitor side voltage and the input direct current of the tractioncurrent transformer in the train traction system are monitored, the distortion degrees of the corresponding net voltage, the corresponding voltage and the corresponding current are calculated according to the corresponding characteristic contents, the backward stage output torque of the traction current transformer is finely adjusted according to the distortion degrees, and accordingly oscillation on the direct current side of the traction system is restrained.