Abstract: It is well known that the deep hole drilling in high gas soft coal seam,hard and soft compound coal seam and outburst coal seam is a worldwide problem,instable failure mechanism of borehole in coal seam is the fundamental and key research to solve above-mentioned difficult problem.Therefore,based on mechanics model of borehole,distribution law of stress field and displacement field around borehole in coal seam was analyzed and discussed by using numerical simulation method,and failure mode of borehole was acquired.Research results show that shear failure is the primary failure mode,"V" type failure and some tensile failure exist in borehole wall,conjugated "X" type shear failure exists in the deep part of coal body around borehole;stress environment around borehole,coalbed gas pressure and human influence are main factors which can impact borehole stability.