The present invention relates to a method and a device for repairing a transistor. The method for repairing the transistor is used for repairing the short-circuit defects of metal layers in the source electrode and the drain electrode of a thin-film transistor. The method comprises the steps of acquiring the short-circuit position of a metal layer between the source electrode and the drain electrode of a thin-film transistor; etching off a protection layer above the short-circuit position by means of a first-wavelength laser; etching off the metal layer at the short-circuit position by means of a second-wavelength laser; and etching off one part of a channel layer below the short-circuit position by means of a third-wavelength laser. Based on the above method, different layers are etched off by adopting lasers different in wavelength, so that other layers are protected. Meanwhile, the channel layer is partially etched off, and a short-circuit defect is repaired to be normal. Therefore, the number of dark spots in a product is not increased at all, and the product yield is improved. The product rejection rate is reduced.