Abstract: The test and measurement of large-aperture optical elements can be made by sub-aperture stitching. The wavefront testing for each area of a largeaperture element under test was performed with a small aperture interferometer, and the wavefront of the large-aperture optical element was calculated according to the sub-aperture stitching results. It is more convenient for large-aperture optical elements to be tested with a small aperture interferometer by sub-aperture stitching method. The simulation of the sub-aperture stitching technology was carried out by the optical design software ZEMAX. The simulated result shows that the relative error of the wavefront testing is less than 4.3λ‰. The high-precision testing for the surface profile of a large-aperture optical element was realized with a small aperture interferometer.