Abstract: Anchor hole drilling is the key link to realize the anchoring, and most of the floor rocks in the roadway of floor heave contain weak interlayer, the physical mechanics characteristics of hole wall are the internal cause of the stability of drilling system when the drill passes through the weak interlayer. Field investigation shows that there is a phenomenon of falling and peeling in the part of the hole wall during drilling anchor hole with weak interlayer, and these large size slag bodies fall to the bottom of the hole, which makes it difficult to discharge slag and affects the quality of anchor hole. Through using the method of combining theoretical analysis and numerical simulation, considering factors such as stress state, drilling power, the hole wall stability of floor anchor hole in roadway with soft interlayer is studied. It is found that the hole wall drilling at the broken soft interlayer position causes the phenomenon of diameter expansion. The stress state has obvious influence on the diameter expansion of borehole, and the influence of drilling power on the degree of diameter expansion is not obvious.