The invention belongs to the field of chemical equipment for catalyst treatment, and particularly relates to an impregnation device and method for a catalyst. The impregnation device comprises an impregnation bed 5, a solution circulating unit and a vacuum unit 15, and the impregnation bed 5 is a vertical fixed bed with unequal diameters, wherein the inner diameter of the upper end of the fixed bed is large, the inner diameter of the lower end of the fixed bed is small, and the outer wall of the fixed bed is provided with a steam jacket 6; and the upper part of the impregnation bed 5 is connected with a catalyst carrier hopper 3, the bottom of the impregnation bed 5 is connected with a tee joint 7, the lower part of the tee joint 7 is connected with a discharging valve 10, and the tee joint 7 is connected with a filter net 9 through a pipeline in the horizontal direction. Decreasing of the concentration of a solution from top to bottom is compensated through the change of the space velocity of the impregnation solution in the impregnation bed with the unequal diameters, and the uniformity of impregnation of the catalyst is improved; and meanwhile, the impregnation device and the impregnation method disclosed by the invention have the advantages that equipment is simple, operation is easy, impregnation is uniform, carrier abrasion in the production process is less, and the impregnation efficiency is high.