通过对比大口径光学元件夹持不当时全口径与局部口径之间的图像关系，研究局部面形控制的新方式。并与高精度的大口径干涉仪进行比对测试，验证拼接干涉仪的测试精度。实验表明，拼接干涉仪局部测试精度可达50 nm（PV值），空间分辨力高达5 mm-1，可以实现中频段的装校监控。使用拼接干涉仪扫描测试全口径面形，测试不确定度小于100 nm，与600 mm的大口径干涉仪测试结果差别小于0.04λ（波长λ=632.8 nm）。

During the assembly of large plano-optics, astigmatism will be generated when the assembly manner is improper. This astigmatism has the same character in local surface and full-aperture surface. The flat stitching interferometer has the ability to measure both the local surface and the full-aperture surface. Therefore, we employ a flat stitching interferometer to inspect local the surface during assembly, by which the astigmatism is controlled. Experiments show that the local surface precision of the flat stitching interferometer arrives at 50 nm (PV) and the space rate reaches 5 mm-1, enabling intermediate frequency detection. On the other hand, the flat stitching interferometer can measure the full-aperture of optics by scanning. The test uncertainty is 100 nm and the difference relative to large aperture interferometer is less than 0.04λ（λ=632.8 nm）.