Abstract: Based on the principle of sub-water sight, the 3D model of urban overground and underground objects was set up in order to solve the problem of visual confusion resulted from modeling directly from their 3D coordinates. According to the principle, when the vision point is located on the ground, a proper color can be given to the earth s surface by using the color blend function of OpenGL, and underground objects are made to have the color ingredient of the earth s surface to distinguish overground and underground objects from their colors. On the condition of great underground depth and more underground objects, information on their depth can be shown by the shading degree of their colors by means of the fog operation function of OpenGL. At last, the feasibility of this method was proved using data on an urban district.