Starting from imaging principle based on diffraction of circle aperture irradiated by point source,the calculation formula of light field distribution of image point with distortion is deduced.The diffraction mechanism and characteristics as well as calculation and correction method are discussed.Simulations show that this theory and method are feasible and helpful to carry out distortion aberration balancing and correction in optical design,as well as detection and correction of distortion in optical processing and electronic distortion correction in digital imaging systems.