Abstract: The terrain physical models are widely used in urban planning, military strategy planning, watershed and geological education, etc. However, current terrain models are mostly stored and displayed by using digital elevation model(DEM) file formats. A method is presented to directly convert the DEM file of a terrain model to the 3D STL Model, which can be processed and fabricated by rapid prototyping(RP) systems. Firstly, various formats of the DEM data are identified and simplified according to the scale and resolution. Secondly, the surface of the terrain is converted to the triangular facets, which are optimized and corrected based on the preset threshold. Finally, the STL model is constructed by adding the base and walls, from which the terrain physical model can be fabricated by a RP machine. A terrain sample with typical topographic feature is selected for analysis. The experimental results demonstrate that the intermediate processes of data conversion are eliminated and the volume of model data is reduced effectively. Furthermore, terrain physical models can be fabricated by RP system in less time and less cost.