The closures determining the interactions of particle particle and gas particle are very important for gas solid flow. A three-dimensional two-fluid modeling approach with the kinetic theory of granular flow is used to simulate the hydrodynamic behaviors of a bubbling fluidized bed and a circulating fluidized bed. The influences of the coefficient of restitution and the drag model on the flow pattern are studied. The simulation results for bubbling beds are compared with the experimental results of Lin et al.(1) It is found that the coefficient of restitution has strong influence on the flow pattern of the particle phase in bubbling beds. A relationship between the coefficient of restitution and the superficial inlet velocity is correlated. The effects of restitution coefficient on the distribution of solid phase in the circulating fluidized beds were also studied. In this case, the influence of the coefficient of restitution is weaker than for bubbling fluidized beds.