Torque multiplier for roof anchor rod

The utility model relates to a torque multiplier for a roof anchor rod. By the torque multiplier, the problem of deficiency of a high-torque construction device which is suitable for the construction of coal mine anchor rods is solved. According to the torque multiplier, a seal and a torque limit device are arranged at the end of the torque multiplier, so that the torque of an anchor rod drilling machine is magnified to a fixed torque value (the error is controlled to be within 5 percent), the pretightening torque of the roof anchor rod can be controlled effectively and accurately, and the torque multiplier is difficult to damage and long in service life; and each torque multiplier can fasten 600 anchor rod, so that the labor intensity of workers is relieved to the maximum limit, and the reliability of the pretightening operation of the large-limit anchor rod is improved.