The invention provides a machine tool clamping device for machining a long-rod-shaped workpiece. The clamping device comprises a machine tool body, first clamps, a machining tool, a translation mechanism and a workpiece reinforcing mechanism, wherein the first clamps are arranged on the two sides of the upper surface of the machine tool body, the machining tool is movably arranged above the machine tool body, the translation mechanism is arranged on the machine tool body and is parallel to the axial direction of the long-rod-shaped workpiece, and the workpiece reinforcing mechanism is arrangedon the translation mechanism; the first clamps adopt first three-jaw chucks; one first clamp is in transmission connection with a machine tool driving mechanism; the workpiece reinforcing mechanism comprises workpiece thickening mechanisms; temperature control mechanisms are arranged on the workpiece thickening mechanisms; a liquid injection mechanism which is movably connected to the workpiece thickening mechanisms is arranged on the machine tool body. According to the clamping device, the precision of the surface of the long-rod-shaped workpiece in the machining process can be guaranteed, particularly, the situation that bending and dislocation cannot be generated in the machining process of the long-rod-shaped workpiece with larger length can be guaranteed, and therefore the precisionof operation such as drilling and threading can be guaranteed to be the highest.