The crushing of the rock is the result of the interaction between the drill bit and the bottom hole plane rock， and the bottom hole stress field is an important factor determining the rock fragmentation effect of the drill bit. In this paper， the finite element numerical simulation method is used to discuss the regular pattern of bottom hole pressure difference on bottom hole plane rock stress under specific ground stress conditions. To consider that reduce the bottom hole pressure can reduce the equivalent stress of rock， changing the stress state of rock， which is conducive to rock breaking by bit. At the same time， it is concluded that the rock near the center of the borehole is the most easily broken， and the rock stress value near the borehole wall is the largest. There will be obvious stress concentration near the borehole wall 0.8R（R is the radius of the borehole）， which makes the rock in this area the most difficult to break. It provides theory basis for the study of the most economical， effective drilling and breakage rock technology.