Abstract: The key to apply CCD to implement mammography is to improve the coupled efficiency of light from scintillation screen to CCD, and it is necessary that the image system has a large relative aperture and adopts close imaging, which makes the CCD image seriously distorted. This paper presents an efficient preprocessing method to compensate image distortion. According to the conjugate relation between the object and its image, the object plane was divided into many micro object elements that have one-to-one correspondence with the pixels of image sensor; Monte Carlo method was used to simulate the light distribution on image plane made by the light from each object element, namely point spread function. A point spread array was constructed from all point spread functions of all elements; each row of the array corresponds to the point spread of function an object element. A linear system of equations to describe the relation between all object elements and all image pixels was built on the basis of the point spread array, and a lifelike image was obtained by solving the linear system of equations. The calculation results for an actual optical system verified the validity of the method.