The fractal interpolation theory was used to the research of road surface roughness, and its simulating method was proposed through the piecewise fractal model. The fractal interpolation model was established for the actual road surface roughness, its influential factors and their laws of influencing were also analyzed, and then the model accuracy was confirmed by the fractal parameters and the traditional parameters. The research indicated that the simulated parameters of road surface in different resolutions and the traditional parameters can keep better consistency with the actual road surface. The contraction factor and the road surface sampling resolution are main influential factors of the model. The contraction factor’s selection decided directly the fractal dimension of the simulated road, and the simulated precision reduced with the decrease of sample resolution at the same time. In fact, this method is able to obtain a better simulation results, as long as the sample resolution was restrained on the scaleless range of road surface roughness.