Large diameter borehole is a commonly used technical method for local relief of rockburst in coal seam. By increasing the borehole diameter and expanding the pressure relief area in the coal seam, the purpose of improving the preventing rockburst effect is achieved. Therefore, a special drilling rig and auxiliary drilling tools are developed for drilling 300 mm borehole in coal seam. The drilling rig has the characteristics of remote control under the coal mine, automatic loading and unloading of drill pipes, and large adjustment range of output parameters, which improves the automation of the drilling rig, reduces the labor intensity of workers, and improves the drilling efficiency of large diameter borehole, The safety during the drilling the large diameter borehole and pressure relief effect of large diameter drilling are improved. The test proves that the parameters of the drilling rig have reached the design targets.