The sky region in the restoration results for dehazing algorithm based on dark channel prior always exists the drawbacks such as halos. In order to further optimize the estimation of transmission function,this paper proposes a transmission function optimization method based on reliability map guided fusion.Firstly,the sky region of the hazy image is segmented and optimized;the window level dark level channel and pixel dark level channel are calculated to ensure the smoothness of the transmission function at the edge of the objects and the outstanding of the detail features smaller than the window size;finally,the reliability map between window level dark channel and pixel level dark channel is calculated.The refine transmission function map is obtained to realize image dehazing by the fusion of these two dark channels through the guidance of the reliability map.The experimental results show that the estimation of transmission function optimized by the proposed method could achieve fine image dehazing effects.