Abstract: The position drifting commonly existed in the actual well drilling process.In the conventional track design,the position drifting influence had not been considered,which increased difficulty to the well trajectory control in the well drilling construction process.The track design method of considering the position drifting influence uses the well section natural curve model,which can reflect the stratum natural deviation and the position drifting rule as well. The produced restraint equation set is ternary nonlinear equation,The usually used numerical iterative method is not easy to assign iterative initial value, convergence performance is bad, the convergence rate is slow. Analytic formula of initial directional angle and section length expressed by steady inclined section deviation angle is inferred, which make ternary equation solution to unary equation with unknown steady inclined section deviation angle and gave numerical iterative algorithm to the equation.The theoretical analysis and the massive actual examples indicated that the new algorithm in the article has good natures of quick convergence rate, small iterative initial value relevance, overall convergence and so on.