Abstract: Since all kinds of noises introduced in the process of the video forming and sampling inevitably lead to a bad quality of video images, the basic principle and algorithm of the median filter are presented to realize the real-time image pre-processing for succeeding processing. The rapid real-time median filter was designed with "flowing technology" according to an algorithm in the fieldprogrammable gate array (FPGA). The method to store the first two lines of the image data in the line output based image processing is given. The simulation result shows that the median filter can implement the real-time pre-processing of CCD output images, and achieve the goal of noise suppression and image details keeping.