Particle dampers have received considerable attention in recent years as a novel damping technique. However, due to its high degree of nonlinearity, no mature damping model has been constructed. This article proposes an equivalent raft model that takes into account both the three-dimensional geometry and the material property. The model is validated by comparing the benchmark results with experimental observations and to simulations using the discrete element method. The equivalent raft model predicts the behavior of the structure-damper system in the presence of ground motion. Additionally, it can compute the time evolution of particles' displacement and force in three different function modes. Moreover, the energy dissipation mechanism of particle damper is investigated using the suggested model to analyze the impact of load amplitude, load frequency, container size, particle mass, and particle material.