According to outdoor images taken under hazy condition, sky area after dehazing is often distorted, based on that, this paper proposes a single image dehazing algorithm combined with sky region detection. Firstly, the atmospheric light intensity is estimated based on the dark channel theory, bilateral filter is used to obtain the atmospheric light and transmissivity map, then sky detection procedure is applied to find whether the sky area is existed in image, the transmissivity is modified according to different results, and finally the restored image is obtained by substituting the fog imaging model. The experimental results show that the proposed algorithm can effectively detect the sky area in image, can modify transmissivity according to modified results and can make the image in the sky region look more natural and smooth and no obvious distortion. It can also improve the contrast of the image without the sky areas which recover more details in the depth of field. This algorithm can receive ideal dehazing effect for all kinds of images.