The invention discloses a toggle-rod type clamping device, which comprises a cylinder. A piston in the cylinder is driven by compressed air to perform a reciprocal rectilinear motion hermetically. The piston drives a clamping arm through a piston rod and a toggle-rod articulated structure. The toggle-rod articulated structure is positioned within a clamping head. The cylinder comprises a cylinder body and a cylinder cover. The piston rod passes through the cylinder cover and penetrates into the clamping head. During the idle stroke, both the side surface of the piston facing the working cylinder chamber, and the side surface of the piston facing the return-stroke chamber, are applied with the same air pressure through a piston slide valve (19). The piston slide valve (19) is longitudinally displaceable and hermetically guided in the hole (17) of the cylinder cover. In order to start the force stroke, the piston drives the piston slide valve to move along the longitudinal axis direction. Meanwhile, gas is discharged out of the cylinder from the side surfaces of the cylinder through a longitudinal channel (24), a branch channel and a channel (16).