Damping matrix of mixed structure no longer satisfies the classical damping condition. In such a case, the modal superposition method may become invalid. The advantage of hysteretic damping model is that energy consumption is related to external excitation frequencies in each cycle. At the same time, the calculation results of time-domain are stable. However, it does not meet the principle of energy conservation. By the equivalence of energy dissipation and damping power in each cycle, damping coefficient of hysteresis damping model can be modified. Subsequently, an improved hysteretic damping model and its own modal superposition method of mixed structure are proposed in this paper. The characteristics of improved hysteretic damping model response spectrum are firstly analyzed. Then, the most unfavorable combination of seismic effects could be calculated. Based on the improved hysteretic damping model, SRSS method for seismic analysis of mixed structure is performed. Results show that seismic effects of the improved hysteretic damping model are more significant than that of viscous damping model, and the increase is about 15%~20%.