The present paper deals with the technique of digital SAR-TM combination as well as the applicability of the combination image for geologic mapping. The process of combination takes on three steps. At first, Six seperate strips of radar data at 3M pixel resolution are mosaiced together to form a 900km² image. Secondly, the SAR and TM data were respectively registered to GaussKruger projection system’ Finally, the false color composite image is produced in following manner: TM4 + SAR(R), TIS + SAN(G), and TM3 + SAR(B). Compared with the original image. Digital SAR-TM combination image has following advantages ; 1 ) The geologic interpretability is enhanced, 2 ) the geometric distortion of terrain featurs is improved, 3) the distinction of the whole image is intensified, because the local shadow area can be diminished due to the supplement of SAR and TM each other. The image of digital SAR-TM combination have abundant remote sensing information. It’ is a powerful tool for geologic interpretation and mapping (on scale 1: 50, 000-1: 100, 000 ).