By analyzing the characteristics of infrared images,the gray space of the image can be decomposed into two parts,one part is from object radiation and the other is from atmospheric radiation. Atmospheric gray factor is proposed in this paper to characterize the gray space generated by atmospheric radiation. In order to improve the image quality and enhance the visual effect of the image,by establishing a grayscale mapping model based on the atmospheric gray factor,the image quality degradation caused by atmospheric radiation is effectively eliminated. As to solve the problem that the edge of the enhanced image is rough,this paper uses the original image as the guide to correct the atmospheric gray factor. Compared with the traditional histogram equalization algorithm,algorithm of this paper has more extensive adaptability. In the meantime,this algorithm can preserve the image detail better while enhancing the image contrast,which is beneficial to further infrared target detection.