The paper proposes a method of image enhancement based on gray-levels in equal distance with interceptive way due to the drawback of histogram equalization with the phenomenon of over-enhancement and gray-levels annexation. The paper intercepts gray-levels using the principle of “3σ”, then, the gray-levels are arranged in equal distance. Finally, the output image is smoothed by median filtering. This method not only enhance image contrast, save image detail, and also overcomes the drawback of gray-level truncation in histogram equalization.