Rough topographic data of granite surface were measured by atomic force microscope (AFM), and the characteristics of this real surface were analyzed according to the topographic data. In the range of geometric optics approximation, the bi-directional reflectance distribution function(BRDF) of this real surface was modeled by Monte Carlo method based on the surface topographic data, where the shadowing effect of incidence and the multiple reflections were considered. By comparing the modeling results of BRDF with its measured results which were measured at the wavelength of 0.6328μm and at different incidence angles, the results show that there is a reasonable agreement between them within a certain error range.