Digital Ecological Model (DEM) is a platform developed with Java. It consists of six components: DEMGIS, DEMTSA, DEMSTA, DEMMOD, DEMVIEW, and DEMAPPLET. DEMGIS features major functions of geographic information system (GIS), such as building digital elevation model, managing geo-referenced database, translating vector data into raster data, and generating geographic graphs with different projections. DEMTSA is used to interpolate the scattered climatic data into raster data, by means of trend surface analysis (TSA) method and interpolation method. As a plug-in for GIS, DEMSTA provides some widely used statistic methods. DEMMOD is a platform for building process-based landscape model. It provides a visual interface-Visual Programming Interface of Digital Ecological Model (DEMVPI) for ecologists to 'write' and record the models in an interpretation language-Ecological Description Language of Digital Ecological Model (DEMEDL). Ecological Model Interpreter of Digital Ecological Model (DEMEMI) is responsible for compiling the programs written in DEMEDL, running the model and displaying the results. DEMVIEW is a tool for viewing and editing some geographic graphs. DEMAPPLET can link a Java applet with geo-referenced database and display the simulation results on the Internet. All the codes of DEM were compiled into Java application programs, and some of the programs are available on the Internet as Java applets. As a case study, amended Penman's method was used to calculate the potential evapotranspiration and aridity index of China, under present situation and three prescribed climate scenarios, which include raising mean temperature by 1.5, 3.0 and 4.5℃, and raising precipitation by 10%, to assess the potential impacts of global climate change on China water condition.