The form of the PSF has been deduced according to the Fresnel diffraction, and it has been analyzed that the frings dens利用菲涅耳衍射理论，推导出相干光照明下无衍射系统的点扩散函数(PSF)的形式，并分析出点扩散函数的条纹疏密与锥镜的夹角和点光源的位置有关。