The information of terrain shadow is an important subject when we study 3D visualization, terrain radiant

correction of remote sensing image, calculation of solar radiation of mountainous areas, etc. This paper deals with

the identification of the terrain shadow based on DEM, which the direct solar radiation creates. The terrain shadow

includes umbra and drop shadow. The methods for identifying the two types of terrain shadow are presented in this

paper. According to the methods, the terrain shadow image of Taibai Mountain area is obtained. In the end, some

important problems are discussed on identifying the terrain shadow.