采用时域有限差分方法，在分析点衍射波前误差的前提下，讨论了点衍射干涉系统中物镜数值孔径、针孔尺寸、检测的数值孔径对衍射光强的影响；逐步优化光学结构参数，得到不同光学结构参数之间的匹配数值表；通过比较点衍射干涉系统和Zygo干涉仪对球面镜的测量结果，得到测量面形误差的均方根之差为波长的1/1000，且获得的干涉条纹具有合适的对比度和亮度，验证了光学结构参数选择的合理性。

On the basis of analyzing the point diffraction wavefront error, the influence of the optical structural parameters, including the numerical aperture of objective lens, the size of pinhole and the numerical aperture under testing, on the point diffraction intensity also have been discussed in the paper. We have optimized the optical structural parameters gradually and obtained the parameters matching reference table. By comparing the measurement results by PDI system and Zygo interferometer, the difference of root mean square error is about λ/1000, and the interference pattern by PDI system have good contrast and brightness, which verify the rationality of the selected optical structural parameters.