A clamping mechanism for a mechanical arm comprises a bayonet pin, a first pedestal, a clamping body, a second pedestal and an elastic body, wherein the first pedestal is fixedly connected to the mechanical arm, is detachably connected to the bayonet pin and is provided with a first through hole which extends in the longitudinal direction; the clamping body is used for clamping an object, is detachably connected to the bayonet pin, is provided with a first magnet, and is suitable for being inserted into the first through hole from the left side of the first pedestal in the longitudinal direction; the second pedestal is detachably connected to the bayonet pin, is provided with a second magnet, and is suitable for being inserted in the first through hole from the right side of the first pedestal in the longitudinal direction; the left end of the elastic body is connected to the first pedestal; and the right end of the elastic body is connected to the second pedestal. When the clamping body and the second pedestal are inserted in the first through hole, the bayonet pin is simultaneously connected to the first pedestal, the clamping body and the second pedestal, and the elastic body is in an elastic stretching state; and when the bayonet pin is separated from the first pedestal, the clamping body and the second pedestal, the clamping body and the second pedestal are connected integrally through the magnetic force of the first magnet and the magnetic force of the second magnet, and elastically move in the first through hole in the longitudinal direction.