Based on the relationship between the rough surface statistics parameters and surface profile fractal parameters, a method for calculating equivalent rough surface fractal parameters was proposed. Furthermore, tangential contact stiffness model was modified. The FEM and modal of the dumb-bell could be obtained when the joint interface was equivalent to the spring elements whose stiffnesses were obtained from the contact stiffness model and evident the effectiveness of the contact model, then the major factors of the modeling accuracy from the stiffness and the numbers of the equivalent spring element was discussed. In addition, the FEM of another dumb-bell was obtained similarly. The frequency response functions (FRFs) of the flexible connection FEM model and the rigid connection FEM model could be obtained from the result of the harmonic response analysis. Through the comparison of the FRFs, the necessity of the research on contact stiffness model was confirmed. 