The utility model relates to a top cover in the technical field of electric power and electricity, in particular to a top cover of a transformer. The top cover is arranged at the top of a transformer shell and provided with a cover plate, downward bending flanges are arranged on the periphery of the cover plate, and a circle of sealing ring locating groove is welded in the pressing and covering face of the cover plate. Due to reinforcement treatment, the overall strength is large, meanwhile, mounting is convenient and easy, the water prevention and dirt prevention effects are good, the service life of the transformer is greatly prolonged, and the top cover is mainly used for the transformer.