Abstract: The forces analysis around borehole can be implicated as plane stress problem in upper bottom of hole, but when nearby bottom of hole, the problem is 3D mechanics because of "end face dugging effect" which has not analytic solution. Through experiment, some regular phenomenon has shown when two horizontul stresses are equal, the stabilization nearby bottom of hole cannot be affected. If the two horizontal stresses are different, the degrees of rock anisotropism under bottom is increased as long as difference increased, so that bit drift towarding maximum horizontal direction.