The invention relates to an O-type ring assembly machine. The O-type ring assembly machine comprises an assembly machine body. A screw plug feeding mechanism is arranged on the assembly machine body,one side of the screw plug feeding mechanism is provided with a material grabbing mechanism, and the other side of the material grabbing mechanism is provided with an O-type ring feeding mechanism. According to the O-type ring assembly machine, screw plugs and O-type rings are quickly fed through the screw plug feeding mechanism and the O-type ring feeding assembly, grabbing is carried out by a mechanical arm when the screw plugs are conveyed to an assembly mechanism, the screw plug feeding mechanism returns to the initial position to feed the next group of screw plugs, the O-type rings are expanded through an expansion mechanism, expanded O-type rings are conveyed to an assembly center, and the screw plugs are moved down to appropriate positions by the mechanical arm to complete assemblyand automatically sleeve the screw plugs with the O-type rings, so that people can be liberated from heavy physical work, and the labor productivity can be greatly improved.