Aiming at the problems that there is dark color and excessive contrast enhancement after image defogging existed in image defogging algorithm based on atmospheric scattering model, a fast image defogging algorithm based on gray correlation degree guided filtering is proposed. Firstly, assuming that the pixels of foggy images could be divided into normal pixels and pixels damaged by haze particles, the gray correlation theory is applied to judge the pixel values of haze images. Then, the pixels damaged by smog particles are guided to filter, the difference between the pixel values of the original image and the filtered image is reduced by taking logarithm, and the fog veil value is calculated in the logarithm domain; Finally, a clear image is retrieved based on the atmospheric scattering degradation model. While Experimental results show that the proposed algorithm could not only effectively improve the clarity of haze images, but also solve the problems of dim brightness and color distortion after defogging.