Abstract: On the basis of the basic principles of excavating method,realizing method of unloading process and finite element theory,by the use of 3D 8-node element and the model for brittleness and nonlinear material,a quarter of bottom-hole model was taken as the simulating finite element model,and three abstracted processes including before drilling,during drilling and after bottom forming were simulated by three time steps.The analytic result showed that radical stress and circumferential stress of rock out of borehole wall were both changed into the original formation stress along radius,and their curves formed a trumpet.The stress in the central area of ω-shape bottom-hole was relieved.The proper application of relieved stress will improve the rock-broken efficiency and rate of penetration of tools.There is stress concentration near borehole wall,where rock's drillability gets worse.It is explained that the side of PDC bits is easy to be damaged.So,more cutters should be arranged on the out side of PDC bits,in order to improve the service life of bits and drilling footage.