Due to the frequent occurrence of haze in recent years, the collection of outdoor images has caused some problems. Image defogging has become a new hot topic. First, Retinex algorithm is studied for fog removal, and four color Spaces commonly used in image processing, including RGB, HSV, RGB and YCbCr, are introduced. HSV, RGB, YCbCr color images are only used for brightness componentdefogging, which picks up the speed. Then, Information Entropy, Contrast, average Luminance and average Gradient that the four indicators are given to evaluate image after fog removal. Finally, Retinex algorithm has the best effect to remove fog in YCbCr color space.