Abstract: Sub-aperture stitching technology can be used for testing large aperture optical mirrors with low-cost and high-precision and without supporting components. Based on planes and high steepness asphere, the algorithm of sub-aperture stitching for shallow asphere was detected. The mathematical model, stitching algorithm as well as the detection process were analyzed and discussed. A shallow asphere was fitted by 37 Zernike polynomials and divided by circular sub-apertures. Then the simulation of the sub-aperture stitching was completed as well as the analysis of the effect of the sub-aperture translation, tilt and random errors on stitching accuracy.