In order to satisfy the optoelectronic equipment′s high precision requirements,the advanced optical system of these instruments became more complex and its alignment became more difficult.Computer-aided alignment proposed as a new method can achieve the system′s alignment fast and accurately.In this paper,possible positions of tow mirrors in the reflective optical system were analyzed and given.The models which are normal parallel in plane,normal perpendicular in plane and normal perpendicular in space,based on the principle of rectangular coordinate transformation were deduced to guide the computer-aided alignment.In the end,the models were simulated by Matlab for supervising the alignment directly.