评估光电系统点目标成像性能或激光远场效果时，通常采用斯特雷尔比作为评估基准，且在工程应用通常采用其近似方法作为分析手段。为更好地分析近似方法的应用范围，有效地指导工程应用，开展了斯特雷尔比近似方法应用极限研究。对常用三种斯特雷尔比近似方法进行了理论推导，给出了其理论基础；依据斯特雷尔比理论，建立了实际像差条件下的斯特雷尔比理论分析方法；从成像评价角度对斯特雷尔比近似方法及其与实际像差斯特雷尔比方法进行了仿真比对分析。结果表明：在波前相位误差小于0.1λ下，近似方法一和近似方法二与近似方法三的误差在10%以内；在遮拦比为0.3、实际像差为球差及相对实际像差斯特雷尔比相对误差优于10%条件下，应用近似方法一时波前相位误差方差需小于0.13λ，应用近似方法二时波前相位误差方差约小于0.1λ，应用近似方法三时波前相位误差方差需小于0.17λ。结果可以给出一定斯特雷尔相对误差条件下的近似方法应用极限，可为点目标成像性能或激光远场效果评估提供技术参考。

When imaging performance of optoelectronic systems to observe point targets or laser far-field effects is evaluated, Strehl ratio is usually used as evaluation criteria, and Strehl ratio is often applied in engineering applications. In order to understand the limits of application field and engineering feasibility, study on the approximate application limits is done. The three approximation ways are deduced, which can supply theoretical basis for the approximations. According to Strehl ratio theory, its accurate analysis method under actual aberration condition is obtained as well. The comparison is done between the approximations and accurate method from the view of imaging. Results show that when the wavefront phase error is smaller than 0.1 wavelength, the error between first approximation and second approximation with third approximation is smaller than 10%. When the obscuration ratio is 0.3 and relative error of Strehl ratio is less than 10%, the wavefront phase error variance must be less than 0.13 wavelength for the first approximation method, the wavefront phase error variance must be less than 0.1 wavelength for the second approximation method, and the wavefront phase error variance must be less than 0.17 wavelength for the third approximation method. The research can apply Strehl ration approximations under certain relative error conditions, which can provide technical reference for imaging performance or far-field laser effects assessment.