A geostress refers to inner stress existing in the earth crust,which is generally constituted by a vertical stress,the maximal horizontal geostress and the minimal horizontal geostress.The heterogeneity or anisotropy of horizontal geostress has been confirmed in many oil fields.Anisotropic horizontal geostress which is generally called confining pressure,has great influence not only on stability of the borehole wall and casing safety,but also on the well trajectory.However,how to evaluate the effect of the anisotropic horizontal geostress on the well trajectory and rocks drillability is a difficult work.In the present paper,the experimental research method was employed to investigate the effect of an anisotropic geostress field on well trajectory and rocks drillability based on the theoretical analysis.The experimental results show that an anisotropic horizontal geostress has obvious influence on drift of well trajectory and rocks drillability.When bidirectional horizontal geostress are uniform,the rocks drillability tends to worse with increasing of confining pressure; the larger the difference of bidirectional horizontal geostress,the better the rocks drillability; in the formation with an anisotropic geostress field,the well trajectory always turns to the direction of the larger compressive stress,and the larger the difference of bidirectional horizontal geostress,the more obvious the drift.