The utility model discloses an oil extraction device for a transformer. The oil extraction device for the transformer further comprises a rotary handle, a support piece and a fastening structure, wherein a sleeve wrench for unfastening or screwing a coupler is arranged at one end of the rotary handle; one end of the support piece is connected with the end part, far from the sleeve wrench, of the rotary handle, while the other end of the support piece is connected with the fastening structure; the fastening structure comprises a first fastening clamp plate and a second fastening clamp plate; the first and second fastening clamp plates are connected to the support piece. The rotary handle is rotated to drive the support piece to rotate, the sleeve wrench unfastens the coupler of the transformer, and the support piece drives the first and second clamp plates to rotate so as to lock a locking nut of the oil extraction device for the transformer, so that the oil leakage phenomenon caused by loosened locking nut of an extraction valve of the transformer in the oil extraction process is effectively prevented, and the oil extraction efficiency is improved.