Abstract: Refract optical system using in remote sensing usually has many elements, complicated structure, and diffraction limited image quality, which makes the assemble puzzled. The tradition way is to alignment each optical element piece by piece, through the device designed to measure the surface tilt error of spherical surfaces with respect to a reference axis. It is time consuming, and worse than all the result is uncertain of successful. In this paper, the method of computer aid alignment was introduced as an assistant to avoid strict process control and reduce the difficulty. A example releases that when a special sensitively variables like distance between two lens is chosen as compensator to reduce the primary aberration after optimization of the optical system, it is effective and convenient to raise the optical system wavefront error RMS from 0.084 (=632.8 nm) to 0.046.