In the fog or haze weather, the scattering of atmospheric particles leads to serious image degradation. This paper proposes a simple and fast algorithm based on physical model to simplify the atmospheric scattering model and obtain a new defogging model. Then it uses the dark channel prior method to estimate the atmospheric light value A, and puts A into a new simplified model to get the fog image. Experiments show that the algorithm is superior to the existing algorithm in processing speed and defogging effect.