传统成像光学系统的点扩展函数（PSF）峰值位置在其光轴上，斯特雷尔比(SR)定义为有无像差轴向PSF强度之比，而波前编码系统在光瞳处相位变化为非旋转对称式，其PSF在像面上将产生偏移，利用PSF的轴向强度计算光学系统斯特雷尔比将不再适用。分析了三次相位掩模板PSF的位置偏移量，其是以焦面为对称轴的抛物线族。并在此基础上提出了适用于评价波前编码系统的非轴向斯特雷尔比(SRWC)，分析了非轴向斯特雷尔比的变化特性，其幅值与相位板参量成反比。并利用非轴向斯特雷尔比研究了PSF的一致性及可恢复性问题，阐述了影响PSF一致性和可恢复性的因素。最后，提出了基于非轴向斯特雷尔比相位板参量的优化方法，该方法给出了相位板参量与系统一致性和可恢复性之间的定量关系。

For general imaging optical system, the peak position of point spread function (PSF) is located in the optical axis. Strehl ratio (SR) is defined as the ratio of on-axis values of PSF with and without aberrations, but PSF of wavefront coding system whose phase change in pupil plane is asymmetric has a shift in the image plane, so evaluation of wavefront coding system using traditional Strehl ratio is not appropriate. Shift value of PSF for cubic phase mask is carried out, which is a family of parabolas, whose focal plane is symmetrical axis. Based on this, non-axial Strehl ratio of wavefront coding system is defined, whose different parameters are analyzed, and the magnitude of Strehl ratio is inversely proportional to parameter of phase mask. Non-axial Strehl ratio is used to evaluate consistency and recoverability of PSF. Finally, an evaluation method in order to optimize phase mask parameter is given, which can determine the relation between consistency and recoverability of PSF and phase mask parameter.