Abstract: In order to improve the detection accuracy of the measurement of large aperture optics stitching, a simple and effective absolute measurement was proposed to amend the system error of the sub-aperture stitching measurements. Firstly, an improved three-flat test was used to obtain the surface shape data of the reference plane and the surface error wave-front based on the Zernike polynomial was established which was used to correct the error of the subaperture measurement data. Then the directly measured values were compared with the full aperture surface stitching results, and the surface error peak value(DV) was reduced from 0.072 1 to 0.028 6 . The results show that the method is effective in reducing the system error that caused by the reference plane and can effectively improve the detection accuracy of the large aperture optics stitching.