The invention discloses an image defogging method based on prior information. The method comprises the following steps: estimating an atmospheric light value according to dark channel prior in combination with distant view dense fog area pixel points; respectively determining atmospheric transmissivity corresponding to distant view dense fog area pixel points and close view thin fog area pixel points according to color attenuation priori; determining atmospheric transmissivity corresponding to pixel points in the close-range mist area according to dark channel prior; determining pixel values corresponding to pixel points of the defogged distant view dense fog area and pixel values corresponding to pixel points of the defogged close view thin fog area; and performing region combination on the pixel values corresponding to the defogged distant view dense fog region pixel points and the defogged close view thin fog region pixel points to obtain a defogged image. By improving the defects of dark channel prior and color attenuation prior defogging algorithms in defogging application, the defogging method has a good defogging effect on mist images in various scenes.