In order to achieve high-precision testing of large convex asphere, a testing method combining sub-aperture stitching and computer generated hologram compensation is proposed. Because the asphericity of the center is small, the direct testing method of spherical wave is used; while the asphericity of the outer ring is large, the method of sub-aperture stitching and computer generated hologram (CGH) mixed compensation is used for measurement. Then, the center testing data and the outer ring testing data are stitched by the stitching algorithm to obtain the full-aperture surface shape. Combined with an example, a large convex asphere with a diameter of 540 mm is measured. The test results were compared with the Luphoscan testing results. The residual error of the two methods to test the RMS value of the surface is 0.019λ, and RMS value after subtracting the self-test aperture and stitching result point-to-point is 0.017λ. The results show that the method can achieve high-precision testing of large convex asphere.