Due to the phenomenon of light absorption and scattering, underwater imaging often has problems such as detail loss, color deviation, illuminance loss, and overexposure. To solve these problems, an enhancement algorithm based on illumination adaptation and wavelet fusion is proposed in this paper. The overall brightness of the image is improved by using the optimized logarithm transformation, and the enhanced image adapted to the background illuminance is generated by the convolution operation of Gaussian kernel function, and then the underwater image is enhanced by wavelet multi-scale fusion to enhance the low illuminance area of the underwater image and suppress the overexposed area. Secondly, by calculating the mean of the color channels, the contrast and color saturation of the fused image are adjusted. Finally, the images after Gamma correction and sharpening are fused by wavelet iteration to obtain the final underwater enhanced image. Experimental results show that the proposed algorithm can effectively enhance image detail and restore image color difference. The mean values of IE, UCIQE and UIQM of the image are improved by 7.5%, 36.6% and 199.8%, respectively, compared with the original image.