This study proposes an underwater image restoration algorithm based on background light estimation and transmittance optimization to address the problem of color distortion and blur of underwater image. The proposed algorithm defines the transmittance as direct and backscatter component transmittances, which effectively improve the integrity of the imaging model. First, the red attenuation component is compensated, and the histogram distribution range is reset to achieve color balance. Second, the best background light point is selected based on the brightness, gradient discrimination, and hue judgment. The transmittance of the backscatter component is then obtained through a red dark channel prior, and the direct component transmittance is obtained through a nondegenerate pixel point. Finally, the two transmittances and the background light are substituted into the imaging model to obtain a restored image. Experimental results show that the proposed algorithm can effectively balance the chroma, saturation, and sharpness of the image, and the visual effect is close to the image in the natural scene.