In order to satisfy the real-time demand of deep space probe map topography of celestial body, an online mobile real-time mapping prototype system based on image stereo vision was designed and implemented in this paper. Stereo images of space object was obtained in real-time by the stereo camera, a group of observed stereo images was used to reconstruct its surface shape, and then the local reconstructed model was connected to generate the whole surface topography model of the space object. The feasibility, accuracy and speed were proved by experiment. The results show that it can meet the demend of real-time mapping.