Abstract: The parameter analysis and simplified response analysis method for passive energy dissipation systems with velocity-dependent dampers such as viscous and viscoelastic dampers are studied by employing the complex damping theory. The complex damping properties are analyzed for the combined damping elements of brace and viscous dampers or viscoelastic dampers in series. The complex damping parameters influencing the energy dissipation effectiveness of dampers in the combined element are determined and the analytical relationship of the parameters and effectiveness is obtained. An equivalent model of the combined damping element is established and a corresponding simplified response analysis method for passive energy dissipation systems with velocity-dependent dampers is put forward. The seismic responses of single-degree-of-freedom passive energy dissipation systems with viscous and viscoelastic dampers are analyzed, respectively, and the simplified method is verified.