The polishing principle of Double-Swing Method (DSM) was introduced, the relative movement characteristic between polishing lap and workpiece was analyzed, and the influence of polishing parameters on the relative movement was discussed. A mathematical model of the DSM in a movement state was established and its movement was simulated in a programming language. Then, simulation effects under different parameters was compared. The shape model of the polishing lap was presented, and the material removal character of the polishing lap with diffident shapes was verified.Finally,a rectangle off-axis aspheric mirror in a size of 224 mm×108 mm was polished by the DSM. The experiment result shows that to manufacture the off-axis aspheric mirror by the DSM can control the middle-frequency error and can obtain high working efficiency, and the surface precision is about λ/30 (rms, @633nm). Therefore, the DSM benefits the development of the manufacture technique for off-axis aspheric mirrors.