A fast and effective single image dehazing algorithm is proposed in this paper because of the low efficiency and the poor result in the sky region on the basis of the dark channel prior． Firstly，according to the color attenuation prior， the scene depth model is established to estimate the transmittance． Then，the rough transmittance is obtained on basis of local consistency and the dark channel prior． After that， the rough transmittance and the transmittance estimated by the scene depth model are fused to correct the transmittance of the sky region． Finally，the image is restored by means of the transmittance refined by guided filter，and the tone mapping is applied to the restored image． Experiments show that the proposed algorithm has high efficiency，which can also effectively improve the visibility and contrast of the restored image．