The invention relates to a press fitting tool for back-to-back outer rings of a tapered roller bearing. The press fitting tool comprises a fixed operation part and a movable operation part capable of moving relative to the fixed operation part, wherein the fixed operation part comprises a centering seat and a centering sliding sleeve which can move relative to the axial direction of the centering seat, the movable operation part comprises a movable pressing head and a guide sleeve which can move relative to the axial direction of the movable pressing head. According to the press fitting tool, as the centering and centering sliding sleeve can move relative to each other, and meanwhile, the movable pressing head and the guide sleeve can move relative to each other, so that the press fitting of two outer rings of the bearing can be realized in one-time assembly. Therefore, according to the press fitting tool, the assembly efficiency of the outer rings of the tapered roller bearing is improved, and the assembly precision and assembly quality of the outer rings of the tapered roller bearing can be greatly improved, so that the yield of the outer rings of the tapered roller bearing is increased.