Abstract: For the purpose to test large aspheric surface by Coordinate Measuring Machine(CMM), the new method combined three coordinate measuring and subaperture stitching testing was proposed. The basic principle and flow chart of the method were analyzed, the synthetical optimization stitching mode and effective stitching algorithm were established based on primary aberration and least-squares fitting. A large off-axial SiC aspheric surface with the aperture of 1 200 mm434 mm was tested by this method with 2 subapertures. For the validation, the whole asphere was also measured by profilometry. The PV and RMS between the two methods is 0.073 m and 0.042 m, respectively; the PV and RMS of residual error is 0.325 m and 0.055 m, respectively.