Aiming at the common problems of mixed noise and fuzzy edge contour in digital images, an image preprocessing algorithm combining modified alpha mean filtering and edge enhancement algorithm is proposed. The modified alpha mean filter algorithm first statistically sorts the pixel values in the pixel matrix, then removes the quantitative maximum and minimum values, and then calculates the average value of the remaining pixels in the pixel matrix.Finally, the average value obtained is used to replace the pixel value of the original center point to achieve image denoising. The edge enhancement algorithm first uses the Sobel operator to locate the edge information of the image, and after extracting the edge of the image, the edge is superimposed on the denoised image, and finally the edge composite enhancement of the image is realized. It has been verified that with the continuous increase of noise density, the algorithm has always maintained a smaller mean square error value than traditional algorithms, and the mean square error growth rate is about 31%.The results show that the proposed algorithm effectively filters out the mixed noise of digital images, enhances the edge information, and satisfies the real-time requirements of the image noise reduction system.