The damping matrix of the complex damping model is easy to be constructed, which only depends on the material loss factor and the structural stiffness matrix. However, the complex damping model has some shortcomings, such as time-domain divergence and causality. Structural inherent characteristics are constant, so that the equivalent relationship between material loss factor and structural damping ratio is deduced and the viscous damping model which is equivalent to complex damping model is obtained. The proposed damping model overcomes the shortcoming of the complex damping model. Besides, the convenience that the complex damping model is directly dependent on material loss factor is retained. According to the equivalent relationship between the material loss factor and structural modal damping ratio, the real mode superposition method based on the proposed damping model is suggested for the proportional damping system. For the non-proportional damping system, according to the equivalent relationship between the material loss factor and modal damping ratio of the substructure, the complex mode superposition method based on the proposed damping model is proposed by the aid of Rayleigh damping and the state space method. The example analysis proves the feasibility and correctness of the proposed method.