A two-way pre-stress clamping device used for a spine implant comprises a screw (1), a U-shaped piece (2), a support (3), a cover plate (5), a pre-stress piece and a clamping connection piece (9). The U-shaped piece (2) comprises a U-shaped piece bottom plate and two U-shaped piece side walls with inwards-protruding transverse pre-stress pieces (4) arranged on the inner surface. The bottom face of the U-shaped piece bottom plate is fixedly connected with the screw (1), and the top face of the U-shaped piece bottom plate is provided with the support (3). The support (3) comprises a two support upper limbs forming a containing groove. The cover plate (5) comprises a cover plate top plate and two cover plate lower limbs. The clamping connection piece (9) comprises a clamping connection piece base and two clamping connection piece lower limbs. A pressing piece (6) is arranged on the lower surface of the cover plate top plate. A gasket (8) is arranged on the upper surface of the clamping connection piece base. The cover plate (5) and the clamping connection piece (9) are connected into a whole through a vertical pre-stress piece (7). The device is easy and convenient to install, multiple clamping guarantees are adopted, the slippage risk of an elastic connection element is reduced, and effective transmission of force between adjacent vertebrae is improved.