在三次相位板的波前编码技术研究中，系统的离焦极限和三次相位板的面型参数是决定系统成像质量和图像恢复难度的重要参数。本文利用根据魏格纳函数推导出的准确波前编码成像系统 MTF函数，提出了一种三次相位板面型参数和离焦极限之间关系的讨论方法，分别利用该方法得出三次相位板系统的理论离焦极限和针对不同应用的实际离焦范围；计算得出限定不同离焦量要求时的三次相位板面型参数的选择。并通过对离焦与非离焦情况下系统 MTF函数对比，讨论系统离焦时的 MTF全局一致性。并分别利用数值计算和 CODE V模拟验证了通过此方法得到的系统离焦极限和相位板面型参数的有效性。

In the wavefront coding researches, defocus limits and the parameters of the cubic phase plates determine thequality of the images and difficulty of restoration. We used the accurate Modulation Transfer Function (MTF) of thewavefront coding imaging system which was obtained through Wigner function to construct a novel function and discussed the relationships between defocus paramount and surface parameters. Through this method, we got the theoretical defocusing limits and the practical defocusing ranges for different systems. At the same time, by comparing the MTF function of defocus system with that of focus system, we discussed the global consistency of the defocusing MTF and tested the selection of surface parameters for different requirements of depth of focus. Finally, CODE V and mathematic calculation were used to examine the defocus limits of an optical system respectively. Meanwhile, the surface parameter for a certain system was offered.