Abstract: Based on fractal geometrical theory, an elastoplastic contact mechanics model for three-dimensional fractal rough surfaces has been established. A modified two-variable Weierstrass-Mandelbrot function is adopted to simulate a three-dimensional fractal rough surface. The existing conditions of elastic deformation, elastoplastic deformation and fully plastic deformation of the single asperity are derived. The relations between size distribution function for all level asperities and size distribution function for each level asperity are developed. Then the relations between the total contact load and the real contact area have been obtained. The results show that:the critical contact areas of a single asperity are related to its geometric size. As an asperity level increases, the height and radius of curvature decrease. As the load and contact area increase, a transition from elastic, elastoplastic to fully plastic contact model takes place in this order and agrees with classical Hertz contact model. The mechanical properties of the rough surface depend on the minimum level asperity and sequential six levels asperities. Other level's asperities have little effect on the mechanical properties of the whole rough surface. Finally, the mechanical model is proved to be reasonable and correct by contact experiment.