The invention discloses a special tool for replacing a rubber ring of an oil drain valve of a transformer. The special tool comprises a top plate, a top bowl with a bowl handle and two screw rods arranged on two sides of the top plate. Tail portions of rod bodies of the two screw rods are respectively screwed with a nut, a casing pipe perpendicular to the top plate is fixedly arranged in the middle of the top plate, the bowl handle of the top bowl extends into the casing pipe, an end face of a free end of the bowl handle is abutted to a top rod head of a top rod screwed in from the other end of the casing pipe, and the free end of the top rod as a connecting end of the handle is exposed outside the casing pipe. After the casing pipe and the top rod are added, the bowl handle of the top bowl extends into the casing pipe and is abutted to the top rod only in a point contact manner. During operation, the casing pipe has functions of both guiding and connecting and relies on the top rod for pushing the top bowl to move forward, what's more, the top bowl and the top plate are in a split structure, influence to axial jacking force of the top bowl due to out-sync screw-in of the two screw rods is relatively reduced, a valve element is not jacked slantingly and furthermore oil leakage of the transformer is not caused.