Abstract: In order to improve the effect of backscattering light on imaging in the conditions of underwater active light illumination, an underwater active polarization defogging algorithm for global parameter estimation based on the fitting function was proposed. First, this algorithm combined with the image enhancement as the image preprocessing. Then, the binary polynomial function was set and the least square method was used to solve the fitting of backscattering light polarization degree variable. Finally, the underwater restored image with higher contrast and richer information was obtained. The experimental results show that the proposed algorithm can effectively improve the underwater image quality in the conditions of active light illumination, improve the image contrast and restore the submerged details. The image enhancement measured value of the restored image is 70% higher than that of the previous algorithms, and it can be applied in medias of different concentrations.