Abstract: The paper puts forward the general concept of DEM first, and then studies the building process of DEM, data collecting process of DEM and data constructing process of DEM. Finally, the use of DEM in a real engineering project is explained, including drawing the sectional drawing, computing the easy cubic mete of the earth, the statistics of surface area in slope, drawing the gird map of three dimensions and computing the surface area, with the paper mainly introducing the drawing of the grid map of three dimensions and the statistics of the surface area of the slope using OpenGL.

Key words: OpenGL, sectional drawing, cubic mete of earth, surface area, digital elevation model