Aspheric surface acts as an important role in optical system. Because of its high precision, large data information and easy alignment, interferometric measurement method based on null computer-generated hologram (CGH) element is widely emphasized in the field of optical metrology and optical manufacture. A paraboloid acting as a special aspheric surface sample is measured in auto-collimated interferometric path by using flats and transmission spheres. Then error data are obtained by means of measuring the same sample with null-CGH in interferometric path. By the calculation of major error data, a conclusion that the measurement uncertainty can reach λ/10（λ=0.6328 μm）which meets the requirement of optical metrology if null-CGH is made in a flat of fused silica with enough thickness.