4D is described and the wide prospects on soil and water conservation are discussed.4D is called as the integrated technology of RS and GIS at 1990’s level， it is the basic mode of digltalized product. 4D include DEM (digital elevation model), DOQ (digital orthophotoquad), DRG (digital raster grapher) and DLG/DTI (digital liner grapher), Which provide real time and precise digitalized product for watershed management.