Image defogging method and system. The method includes: acquiring minimum intensity values corresponding to pixels in a foggy image, and selecting the largest values of intensity values of R, G, and B channels of pixels in an area, covered by a brightest area of a predetermined size in a local minimum intensity image, in the foggy image as component values of R, G, and B channels of an atmosphere light value; acquiring a transformation image of the foggy image with atmosphere light value of the foggy image; acquiring a transmission map of the foggy image by edge-preserving filtering the transformation image; and acquiring intensity values of R, G, and B channels of pixels in a defogged image using transmission map and atmosphere light value of the foggy image and intensity values of R, G, and B channels of pixels in the foggy image.