A clamp device for an automobile steering knuckle is composed of a machine tool (1), fixed bolts (2), a hydraulic cylinder fixing seat (3), the steering knuckle (4), a hydraulic cylinder piston rod (5), a movable end (6) and a clamping block (7). The other end of the hydraulic cylinder piston rod (5) is connected with the movable end (6). The clamp device is characterized in that firstly, the movable end (6) is kept away from the hydraulic cylinder fixing seat (3), then the steering knuckle (4) is arranged on the step of the hydraulic cylinder fixing seat (3), a hydraulic cylinder is started, the movable end (6) moves downwards under the action of the hydraulic cylinder piston rod (5) and is gradually close to the upper surface of the steering knuckle (4), and finally the aim of fixing and clamping the steering knuckle (4) is achieved. According to the clamp device, the movement of the movable end (6) and the hydraulic cylinder fixing seat (3) is driven based on a hydraulic transmission principle, a workpiece is automatically clamped and located, hand labor intensity is low, time and labor are saved, and work efficiency is improved. Locating is accurate, product quality is good, work efficiency is high, and the clamp device is especially suitable for clamping and machining automobile parts with middle holes.