Large convex aspheric mirrors are widely used in optical system, especially for off-axis three mirror systems as secondary mirrors. Considering the mechanical and thermal properties, SiC is chosen as the material of the mirror, which is opaque. For off-axis optical system, the full aperture of the secondary mirror is used for imaging. Because of the properties of large convex aphereric mirrors, such as large aperture, opacification and no obstruction in the optical system, testing of this kind of asphric mirrors can′t be accomplished with traditional method. To solve the testing problem, hybrid compensation testing method with computer-generated hologram (CGH) and fold sphere is proposed, and an alignment method based on the assistant areas of CGH is proposed too. With actual project, a φ120 mm mirror is tested using hybrid compensation testing method. The testing result is the same with the stitching testing result at 1/50 λ root mean square (RMS), which proves the feasibility and validity of the hybrid compensation testing method.