针对表面高度均方根(RMS)难以描述大尺度波动以及刚体位移鲁棒性差的缺点，提出了使用功率谱(PSD)对大口径望远镜系统中主反射镜面形进行评价; 结合Zernike多项式，对PSD的分解运算进行了分析，讨论了Zernike多项式的频谱能量分布; 将该方法用于Φ500 mm反射镜面形检测数据的处理，得出实际反射镜表面面形频域能量分布情况。结果表明：对于大口径反射镜，使用PSD的评价方式对于指导加工检测以及望远镜系统误差的分配具有更实用的意义。最后，基于PSD提出了一种评价反射镜面形的子孔径非相关拼接方法，该方法适用于大口径望远镜中大口径光学元件的面形精度评价。

Firstly, Power Spectral Density(PSD) is proposed for mirror surface figure evaluation in the large aperture telescope system as for some difficulties for Root Mean Square(RMS) in the evaluation of large scale variety and disadvantage of robust for rigid body displacement. Then, the decomposition arithmetic of PSD is analyzed with Zernike polynomial, and Zernike polynomial spectrum energy distribution is analyzed in some order. The algorithm has been used in the surface figure evaluation of a Φ500 mm mirror, and energy distribution in the frequency domain of the actual mirror surface has been obtained. The experimental results indicate that the evaluation of PSD is more practical when used in large aperture mirror for their manufacture and testing and for the error budget allocation in telescope system. Finally, a kind of noncorrelative sub-aperture stitching method for evaluation of reflective mirror shape based on PSD is proposed which can be used in the large aperture telescope.