Abstract: Destressing with drilling boreholes has been widely used for coal burst prevention. The effect of small diameter boreholes may not be significant. In this study,an equipment for drilling 300 mm diameter boreholes has been developed and used for destressing. The results show that the ZDY20000LK drilling rig has the ability to drill 300 mm large diameter holes at one time,and can be operated remotely by using the video monitoring system,which greatly improves the construction automation level of the drilling rig and the safety of operators. The effect of weakening coal and rock mass by 300 mm boreholes is 18.5% higher than that by 150 mm boreholes. The effect of weakening coal and rock mass with 0.6 m hole spacing is 7% higher than that with 1 m hole spacing. It can be seen that increasing the hole diameter can improve the distressing effort to a greater extent. After a week of pressure relief by 300 mm boreholes,the medium burst risk area outside the roadway surrounding rock support area basically disappearred,and the area of weak burst risk area decreased by 89.7%. In the support area,the decline percentages of burst risk areas were 85.8% and 91.2%,respectively. The field test shows that the prevention effect of drilling large-diameter borehole within the coal seam has been significantly improved.