Abstract: If the distribution of the control points is asymmetric or the model is over parameterized,the problem of ill-conditioned normal equation easily occurs during solving the rational polynomial coefficients(RPC) of satellite imagery.Traditional least squares adjustment can't get reliable solution.Ridge estimation is introduced to ameliorate the condition of the normal equation and to ensure that the solution is reliable.The basic principle of solving RPC by using ridge estimation is introduced.SPOT and QuickBird imagery are processed by different regularization techniques.The empirical results have verified that L-curve method is a reliable and valid way for choosing the ridge parameter,and it could improve the accuracy of the solution distinctly.