Due to the special structure of non-o rthogonal axes (N-Theodolite),the parameters of the sight axis of the N-Theodolite may change slightly after transportation or being used for a long time.Such subtle variation will result in a great decrease in measurement precision.So it is nec essary to correct the sight axes to guarantee the measurement result and thus make the instrument more practical.To solve the problem,this paper proposes a correction method for the sight axis ba sed on forward intersection of N-Theodolites.The method uses the intersection constraint to e stablish the equations for the parameters of the sight axis and the parameters can thus be ob tained by solving the equations.To verify the method,simulations based on SolidWorks software and Open GL are conducted,and the experiments using N-Theodolite are also performed.The simulation results show that the method can effectively correct the parameters of the sight axis with high pr ecision.In the experiment,after correction,the N-Theodolite system can measure the length of the standard scale bar with the same precision of the N-Theodolite system with correct sight axes parameters. Moreover,the sight axis can be corrected in the field because the method doesn ′t involve other precision instruments.