In recent years, Geographic Information Systems (GIS) have gradually changed from using the traditional 2D map expression to 3D visualization. The combination of visual techniques and GIS is a multi discipline, leading edge field, the development of which needs advancement in many fields. This paper introduces related theories and algorithms of Digital Elevation Model (DEM) visualization. Advantages of the Triangle Irregular Network (TIN) model and data structure are illustrated. The algorithms include the visualization process and methods to increase the realism of the DEM. Illumination models and a special technique to map remote sensing images onto DEM are also presented.