In the raster scanning radar display system，the simulation of afterglow effect in the random scanning radar display system is an important unsolved problem in up-to-date radars. This article introduces a new type of radar display system in raster scanning mechanism as well as the method to realise ofterglow effect. Based on the theory of Pseudo-random sequence, the simulation of afterglow effect in the random scanning radar is accomplished and a perfect simulation effect will therefore be achieved by means of using a shift memory to create a random address generator，using a high-speed read-only memory (PROM) to trace data，and perform the reading，revising and writing process on video memory (VRAM) so as to decrease the video data progressively.