Abstract: A new method of median filter algorithm based on the last frame is proposed to meet the demands of real time image preprocessing. It makes full use of the relative information of adjacent windows to finish the median filter processing by arranging only the added column (or row) of pixels with the rest of the arranged pixels remaining unchanged when one column (or row) of pixels is deleted and another column (or row) added. It has been proved that the new algorithm can well reduce the complexity of traditional median filter algorithm from O(D 2) to O(D) . Its results of application turns out to be satisfactory.