A drag model based on energy minimization multi-scale (EMMS)approach was used in the numerical simulation for fast fluidized bed (FFB)containing Geldart A particles.The Johnson and Jackson boundary conditions (BCs)were used for solids phase.The experimental conditions of Li and Kwauk were adopted in the simulation and two inlet BCs were used to evaluate its impact on the predicted gas-solids two-phase flow characteristics in term of axial voidage profile，outlet solids flux and solids holdup.Axial voidage profile was also investigated with different bed diameters and outlet constraints.It was found that it needed less simulation time，and could diminish the cost of simulation for cycle inlet BC than velocity inlet BC.Increasing bed diameter could result in weakened wall influence，and decrease in bed density and heterogeneity of axial profile.The enhancement of outlet constraint could lead to an increase in bed density.