Abstract: From the statistic and comparison of electric logging inclination in the actual wells drilled and the seimic data in the south west area of Sichuan,the formation natural building law in this area is thoroughly studied,and from the view point of stratigraphic and mechanics,the action and mechanism of the formation natural building is discussed,and the method for predicting well deviation and easy calculating equation are proposed.The studies consider that the drilling in the inclined formation,through the quantitative prediction of deviation value,it is quite possible to orientate the well bore toward the target relying on the formation natural building law by changing the determination of well location according to the traditional location of verical well into moving the well to an appropriate distance along the opposite direction of formation natural building.From the drilling practices of 4 wells in south west area of Sichuan,the target is satisfactorily reached and good economic effect is obtained.