Using the remote sensing technology in archaeology, the authors carried out general researches on the old river courses and old cities in the Sanxingdui site by processing and interpreting Landsat ETM+ data and aviation data. The results were compared with each other, and some formerly undetected old cities and old river courses were discovered from south of the Mamu River northward. It is thought that old Sanxingdui city had two layers, one was outside the city whereas the other was inside the city. The authors provide a scientific basis for sustainable establishment of cultural relic protection and make some suggestions to help the department of cultural relics in planning and programming old cities.