The borehole instability problemsareserious inKeshen fractured reservoirwith largeburied depth in Tarim Basin.It is very important to establish the method of evaluating the stability of the borehole wall with anisotropic formation in this area.Throughstudies on the correlation of site wall instability and formation weak surface, the existence of the weak plane made the rocks damaged before the rock mass under the background of strong stress and high pore pressure, it will be broken easily and cause collapse and sticking. If the fracture permeability is good, loss may occur when drilling fluid pressure is greater than pore pressure, then loss pressure is no longer controlled by fracturing pressure and minimum horizontal principal stress, but on the relationship between the occurrence of fractures and the triaxial stress state. So for the formation of strong anisotropy, the collapse pressure and loss pressure of weak strength plane is the key parameter in the evaluation of drilling stability. As the main controlling geological factor of the borehole instability in this area that is the failure of the weak surface of the crack under the strong stress background was determined, the stability of the mechanics of transverse anisotropic rock mass was evaluated in Keshen area, a method for evaluating the stability of wellbore under the complex condition of strong anisotropy was established in this paper. Quantitative calculation of safety mud density windows of fractured reservoirs is generally narrower or even without theoretical safety windows in Keshen. The study shows that the wellbore instability be reduced by improving the performance of the mud or using a directional well drilling scheme. The field practice shows that after the drilling fluid density is adjusted to a reasonable range, the instability of the wellbore is obviously reduced, and the complex problems in the field are effectively solved.