Abstract: The existence of complex multi-scale, multi-physics and nonlinear behaviors on joint interfaces is mainly response for complex dynamics of assembled structures. Modeling of mechanical joint interfaces is also a challenging scientific problem, due to the complexity of interface behaviors and difficulties of direct experimental observation. Firstly, the multi-scale physics of contact surface is considered. The namely smooth surface is assumed as a rough surface covered with asperities with random height distribution. The micro-scale stick-slip physics of asperity contact is analyzed to conduct the relationship between the tangential load and deformation. The statistical theory of GW model is used to yield the formulation of total contact load of rough surface and verified by a comparison with published experimental results. Then, an improved Iwan constitutive model is proposed to describe the nonlinear behaviors of joint interface. The nonlinear behaviors calculated by the finite element analysis are used to identify the parameters of proposed Iwan model, and verified by a comparison with the results of finite element analysis. The results show that the total contact load of rough surface predicted by the proposed multi-scale model agrees very well with the experimental results at lower normal load. The nonlinear behaviors predicted by the proposed Iwan model also agree very well with finite element analysis.