This paper proposed an improved gradient smoothing boundary algorithm for the ringing effect generated by coded aperture imaging in image restoration. As the first step, the blurred image is filtered by means, and the gradient smoothing image is calculated. Then the image is extended by reflection interpolation, and the preprocessed image is obtained by the optimal window processing. Finally, the original image is restored by the improved Wiener filter algorithm. Experimental results suggest that the improved algorithm can effectively suppress the ringing and retain the details of the image. Compared with the gradient smoothing boundary algorithm, the structural similarity of image restoration is improved by 27% and the image quality index is increased by 19%.