A jack structure for a clutch contains a main hydraulic cylinder to push a movable arm to move vertically, and a holder including a support rod actuated by an auxiliary hydraulic cylinder of the movable arm to move vertically and horizontally relative to the holder. The main hydraulic cylinder is a single acting hydraulic cylinder, and the auxiliary cylinder is a double acting hydraulic cylinder. The main hydraulic cylinder communicates with an inlet tube of the auxiliary hydraulic cylinder. A valve seat includes a pump hole to draw hydraulic oil via a valve seat cylinder, an inlet connected with the inlet tube, an outlet coupled with an outlet tube of the auxiliary hydraulic cylinder, and a bore connected with an oil tank. A control post is axially connected with the valve seat and includes plural grooves to selectively communicate with the pump hole, the inlet, the outlet, and the bore after rotation.