The invention relates to an auxiliary device for installing a large-scale snap ring which comprises a base structure, an inserted pin support device and a snap ring support device, wherein, the inserted pin support device comprises a plurality of big upright post tubes fixed on the base structure, a plurality of small upright post tubes are respectively inserted in the big upright post tubes in a movably matching manner, and the upper ends of the small upright post tubes are fixed at the bottom part of a workbench; a plurality of adjusting screw rods are respectively inserted in the rest of the big upright post tubes in a movably matching manner, adjusting screw nut are installed on the adjusting screw rods corresondingly, and the upper ends of the adjusting screw rods are fixed at the bottom part of the workbench; the snap ring support device comprises a plurality of small round tubes, upper boards and a plurality of movable supports, wherein, the small round tubes are fixed on the base structure, the upper boards are installed on the small round tubes, and the movable supports are installed on the small round tubes; and a lower board is fixed on each movable support. The the invention, the work efficiency for installing the large-scale snap ring is improved, the labor intensity is reduced, human resources and material resources are saved, and the potential safety hazard during the installation process of the large-scale snap ring is eliminated.