The second-order (defocusing and astigmatism) error of the reference surface is the major factor that results in accumulated stitching errors, whereas the higher-order errors of the reference surface will result in high-frequency shape errors. Subsequently, the law of stitching errors caused by the second- and higher-order errors of the reference surface is analyzed, and the relation between any two subaperture stitching errors that can be attributed to the reference surface error is studied. Further, an algorithm is proposed to effectively reduce the influences of the higher-order errors of the reference surface on the subaperture stitching results. The stitching errors of the higher-order errors of the reference surface are isolated using this algorithm to eliminate the stitched surface data of any two subapertures. Furthermore, the validity and effectiveness of this algorithm are verified using simulations and experiments.