The invention belongs to the assembly technique of assembly of parts for valve cores, and particularly relates to a tool for preventing a rubber gasket from being damaged by via-hole installation. Thetool comprises three parts of outer embracing blocks (2), core rods (1) and pins (3), the core rods (1) are consistent with valve cover via holes in radius, one end of each core rod (1) is an arc face, and the radius of the arc faces is consistent with that of valve cover inner holes; the core rods (1) are inserted into cooperation holes of the outer embracing blocks (2), one ends of the outer embracing blocks (2) are arc faces, and the radius of the arc faces is consistent with that of the external circle of a valve cover; pin holes are formed in the core rods (1) and the outer embracing blocks (2) and fixed through the pins (3), so that the arc faces of the core rods and the arc faces of the outer embracing blocks are concentric and coaxial. The tool is simple in structure and easy to operate; the working efficiency is greatly improved, and the rubber gasket of a valve core is effectively prevented from being damaged.