Abstract: A two-dimensional digital image based on numerical modeling method for heterogeneous geomaterials was presented. The granite was used as an example for the present investigation. First, the actual heterogeneities of granitic rock surface were extracted from color image by applying image processing techniques. Then a simple linear transformation was proposed to transform the actual image data into vector square data for generation of finite meshes or grids. Finally, the vector data were incorporated into the traditional numerical methods, such as finite element method and finite difference method for numerical simulations. A finite difference software package FLAC was used to study the rock failure process. Three typical laboratory tests were simulated to examine the influences of material heterogeneities on stress distribution and failure patterns. Numerical results show that digital image based numerical modeling method can be used to calculate the mechanical responses of geomaterials by taking their heterogeneities into considerations.