If the histogram equalization on the basis of Retinex theory is used to an image, an excessive enhancement or darkening of brightness may arise. Aimed at these problems, this paper presents a parabolic adjustment of image clearness algorithm, which is mainly based on Retinex theory, equalizing histogram with the aid of parabolic transfer function, while stretching the contrast of image. Experimental results show that the proposed algorithm can make image more detailed, contour smoother, the whole image clearer and the visual effects more optimized.