A fractional Fourier filtering model for an imaging system is established on the basis of partially coherent imaging and fractional Fourier transform theory and a corresponding fractional-Fourier domain preset-phase iteration ( FrPi) algorithm that can quickly design fractional domain phase filters is proposed. 基于部分相干成像和分数傅里叶变换理论,建立成像系统的分数傅里叶域滤波模型,提出了可快速设计分数域位相型滤波片的FrPI算法。