The invention discloses an air-cylinder-type clamping mechanism for machining of an automobile rocker shaft. The air-cylinder-type clamping mechanism comprises a rack; a storing fixing plate is fixedto the middle of the top face of a top plate of the rack; clamping air cylinders are fixed to the front portions and the rear portions of the two sides of the storing fixing plate correspondingly; pushing blocks are fixed to push rods of the clamping air cylinders, and clamping blocks are fixed to the opposite wall faces of every two pushing blocks which correspond in the left-right direction; arc-shaped grooves are formed in the opposite wall faces of every two opposite clamping blocks; and the to-be-machined shaft is arranged in the arc-shaped grooves in inserted and sleeved modes and clamped among the four clamping blocks which correspond to one another. Vertical plates are fixed to the front portion and the rear portion of the top face of the top plate of the rack correspondingly; limiting clamping air cylinders are fixed to the wall faces, away from each other, of the two vertical plates correspondingly; pushing rods of the limiting clamping air cylinders penetrate through the vertical plates and are fixed to end limiting plates correspondingly; and positioning blocks are fixed to the opposite wall surfaces of the two end limiting plates correspondingly. The air-cylinder-typeclamping mechanism can be mounted on a drilling machine, the to-be-machined shaft can be automatically clamped and fixed, and thus drilling of the drilling machine is facilitated.