As a kind of aspherical surface, off-axis aspherical surface is an indispensable optical device for space optical systems, astronomy and high-precision measurement system. In response to the significant demand of manufacturing technology of large-scale off-axis aspheric optical components in space optics, researches on precision grinding technology of off-axis aspheric mirrors have been carried out. The principle of grinding off-axis aspheric surface using generating method in a five-axis machine tool is analyzed. The coaxial parent mirror where the off-axis aspheric surface locates is divided into a series of spherical rings with different radii, and the workpiece coordinate system is established at the center of the coaxial parent mirror of the off-axis aspheric surface to be machined. The cup wheel grinds each ring on the coaxial parent mirror in turn, and the off-axis aspheric surface is formed by splicing some of the rings. Based on this method, an off-axis parabolic mirror with the aperture of 100mm is sucessfully machined.The width of the divided rings is set to 7.28mm. After one process which takes only 7 min, the PV value of the surface error reaches 7μm, and the RMS value of the surface error reaches 0.622μm.The experiment proves the feasibility of this method and provides an effective solution for off-axis aspheric rapid grinding.