The spouted bed has been used in the coating process of high-density nuclear fuel particle. The particle fluidization behaviors in pseudo-2D and 3D spouted beds were simulated and validated. The effects of four independent variables (cone angle, particle density, inlet gas velocity, and particle loading) on particle fluidization behaviors in the 3D spouted bed were investigated systematically. The cone angle effect on fluidization mechanism was studied quantitatively first time. A new fluidization quality index was proposed based on the particle entrainment principle, and an extreme value was obtained when the cone angle was 60°, considered to be the optimum value for the 3D conical spouted bed. It was indicated the gas–solid contact efficiency can be kept up if the gas velocity was proportional to ρ_p^0.65 and N_p^0.78 when the particle density or loading was increased. These results will be useful for geometry and operation parameters design of the 3D conical spouted bed and helpful for developing the fluidization mechanism of high-density particles.