Abstract: In order to solve the problems of poor visual effect, unclear image and insufficient detail display in low-illuminance image, an improved Retinex algorithm based on guided filtering is proposed. Guided filtering was used to process low-illuminance image, and brightness component was enhanced adaptively, and weighted fusion was performed according to the characteristics of sub-image. It could not only preserve the details of the edge part of the image, but also suppress the "halo" of the local highlight area while enhancing the brightness of the dark area of the image. Through a lot of tests, the improvement of the algorithm is obvious not only in the subjective visual effect, but also in the peak signal to noise ratio (PSNR) and structural similarity (SSIM).