Taking ERS-2 and satellite Radarsat-1 radar data as the main information, this paper discusses the regional geological mapping units on radar image in the regional geological mapping (1∶250000 scale) of Daheishan sheet in Xinjiang. The changing regulations among echo intensity and topography units and the lithologic characteristics are summarized, and the relationship between echo intensity and roughness is analyzed. The results show that the gray shade of pixels in the radar image can represent special geological mapping units, and different gray units can be used as basic ones in regional geological mapping. The authors have studies the methods and techniques when the radar image is used as the key information source in regional geological mapping. The results obtained can offer technical support for SAR technique applied in 1:250000  regional geological mapping.