In order to improve the clarity and visibility of underwater images, an algorithm based on the combination of differential channel gain and improved multi-scale Retinex algorithm is proposed to improve the quality of underwater images. First, considering the strong attenuation of red light by the water medium, the improved gray-scale world method is used to gain the red channel separately to make it closer to the uniform lighting scene. Second, in order to eliminate foggy blur and enhance the contrast of details, the improved multi-scale Retinex algorithm processes the image after the difference channel is enhanced, and replaces the logarithmic function in the multi-scale Retinex algorithm with the tanh function to reduce the loss of data and ensure the integrity of the information. Finally, the adaptive gamma technology is used to adjust the brightness of the image distributed. Experimental results show that the image processed by the proposed algorithm is clear, natural in color, and has better visual effects.