Current situation of single image defogging method are introduced,some classic algorithms based on image enhancement and image restoration are analyzed in detail,and advantages and disadvantages are listed in this paper.Comprehensive evaluation results show that the image restoration method is superior to the image enhancement method in the aspect of defogging. Aimed at the existing image restoration defogging method, thorough investigation and study are needed, and some problems about how to break through key technologies in defogging are analyzed from the establishment of a comprehensive physical model, the exploration of a prior knowledge of the model solution, the design of model solution methods based on human visual mechanism, and the evaluation of image defogging quality and some other aspects, etc.. Finally, the development trend of the existing technology is analyzed, and the orientation of studying defogging technology is given.