The utility model provides a preloading device of belt antithetical couplet group, includes cylinder, support arm, ejector pin, motor, box, singlechip and pressure sensor, the cylinder is by steel sheet coiled hollow cylinder, erects through the center pin and puts in the bearing at support arm both ends, the axle of motor is concentric with the ejector pin, ejector pin and bracket connection, and longitudinal motion is made along with the motor shaft to the ejector pin, supports the armlet and the cylinder to the belt application of force, the box is equipped with motor and singlechip, pressure sensor has been buried underground in support arm both sides, pressure sensor with the singlechip that sets up in the box links to each other. The utility model discloses preloading device of belt antithetical couplet group has solved frequent firm and the problem changed in the belt use, can control specially adapted beam -pumping unit belt firm, the single chip microcomputer control mode of adoption, automatic control belt atress size, the problem that influences belt life and belt creep of having avoided that artifical fastening results in to different batch belts equally respectively.