The utility model relates to a vacuum oil filling device for a transformer. The transformer is entirely placed inside a vacuum container, a threaded blind hole is drilled on the flange end surfaced of the insulated cylindrical transformer, and a threaded silicon sheath is arranged in the blind hole. Through the threaded blind hole drilled on the flange end surfaced of the insulated cylindrical transformer, the oil mist is gathered in the blind hole, so as to avoid seepage of the residual oil in the hole along with the extension of time, facilitate centralized cleaning, avoid contamination flashover after adhesion of dust and oil stain, and ensure normal operation of the transformer equipment. The threaded silicon sheath arranged in the blind hole can enhance the strength of the blind hole and has better insulating effect.