Abstract: This paper introduces three key technologies of direct drilling, such as straightening technology, slag discharging technology and backdrilling technology. Aiming at the problem of the deviation of the drilling hole for gas drainage in coal mine, a device for straight drilling of coal mine gas extraction borehole is developed. The structure and technical parameters of direct drilling unit are described. Considering the tolerance stress strength of the device, the material is optimized for the drill pipe joint and drill pipe body, and the torsion strength is calculated.