The invention provides a boss clamping device, which belongs to the technical field of mechanical processing. It includes a pressure plate, a cam, a claw, and a rocker. The fulcrum is a stepped shaft. The diameter of the middle end of the fulcrum is larger than the diameter of both ends. On the support, the pressure plate passes through the rectangular groove at the middle end of the support shaft, the pressure head is set at the lower left end of the pressure plate, and the lower side of the right end of the pressure plate is also provided with a transverse groove and a cam support groove, and the cam is fixedly installed on the camshaft, and the cam and the cam of the pressure plate The supporting groove fits together, and the side of the cam is also equipped with a claw that matches the shape of the transverse groove. The lower end of the rocker is installed on the camshaft through a lock nut, and the left end of the piston rod that drives the cylinder and the upper end of the rocker pass through the support pin. Shaft hinged. The present invention sequentially realizes that the pressing plate advances, then clamps the hem, then lifts and releases, and finally completes the retreat action, which is beneficial to the feeding, processing and unloading of the boss, and has reasonable structure, low cost and good reliability.