To promote the application of non‐stacked particle damper (NSPD) in civil engineering, a design methodology was suggested on the basis of the double inert mass equivalent model. NSPD single‐story steel frame model is selected as the research object in this paper. First, the analytical solution for the periodic motion with symmetric two impacts was discussed. The shaking table test was performed to verify the rationality of the analytical solution under harmonic excitation. Subsequently, based on the analytical solution, the influence of equivalent connection stiffness on the vibration reduction effect and mechanism was analysed under resonant and non‐resonant harmonic excitation. The numerical analysis methods of the optimal equivalent connection stiffness were obtained accordingly. Finally, the effectiveness and generalization of the proposed optimal equivalent connection stiffness were discussed numerically under harmonic excitation and seismic ground motion. An optimal design process for the NSPD was proposed accordingly. Based on this, the vibration reduction performance analysis of NSPD under far‐field records, near‐fault pulse‐like records and near‐fault non‐pulse records was further conducted in the end. The results show that the time‐dependent frequency behaviour of the uncontrolled structure has a significant impact on the performance of the NSPD. The proposed optimization method is effective, which can be used as the foundation for the optimization of NSPD under earthquakes.