Abstract: In geodesy many models are nonlinear ones. The classical methods dealing with these nonlinear models are either linear approximations using the approximation value of parameters or iterations. Some nonlinear models can not be linearized. Linearizing these nonlinear models will reduce the precision of estimators. If using iteration there is different convergence for differents methods or for different nonlinear modes. And it is very difficult to evaluate precision of estimators or functions of estimators. To solve the problems,a direct solution method has been presented in this paper. The influence of quadric term and cubic term has been taken into consideration. The method is an effective and rigorous one. The precision of estimators can be evaluated by classical method in the method. And estimators obtained by the method have fine statistic characters.