计算全息元件(CGH)可实现光学非球面的零位干涉高精度检测，但深度非球面的非球面度以及非球面度梯度均较大，使检测所需CGH的局部空间频率偏大，加工困难。提出一种用组合CGH检测深度非球面的方法，该方法通过组合两个低空间频率CGH，实现深度非球面检测时所需的单个高空间频率CGH的功能。由一维线性光栅模型推导组合CGH与传统单个CGH空间频率的关系，并由此给出组合CGH初始相位，逐步优化可求得最佳相位。以最大非球面度193.434 μm、最大非球面度梯度75.788 μm/mm的深度非球面为测试样例，设计了单个CGH和组合CGH，残留波前误差均小于λ/250，组合CGH最大空间频率约为单个CGH的50%。设计了辅助装调CGH减小装调误差的影响，并分析了组合CGH之间俯仰倾斜偏差、中心偏差以及轴向定位偏差对检测精度的影响。

Null interference technology based on the computer generated hologram (CGH) has been used to measure the aspheric surface. For measuring deep aspheric surface with great deviation degree and high slope, it is difficult to fabricate CGHs with high spatial frequency. We proposes a method combining CGHs with low spatial frequency to achieve the function of a single high-spatial frequency CGH in deep aspheric surface test. A one-dimensional linear grating model is introduced to establish the relationship between the spatial frequency of the single CGH and that of CGHs combination, and the initial phase of the CGHs combination can be obtained based on the relationship. The optimal phase is solved out by optimization. For the deep aspheric surface with maximum departure of 193.434 μm and slope of 75.788 μm/mm, the wavefront errors for the single CGH and the CGHs combination are less than λ/250. The maximum spatial frequency of CGHs combination is reduced by 50% compared to that of the single CGH. Auxiliary alignment CGH is designed to reduce the adjustment errors, and the influence of tilt error, decentration and axial deviation on the detection accuracy is analyzed.