Entire 3-D numerical simulation was used to study the experimental device of miniature biomass circulating fluidized beds gasifier(CFBG). Mutual influence of each unit was taken in consideration in simulation. Euler dual fluid granular model, particle pulsation theory and Gidaspow momentum exchange model were used. The simulation showed the variations of 3-D gas-solid flow structures and distributions at different solid inventories. It formed a pressure loop over the height of reefed line orifice, and performed large scale axial circulations. It could not form obvious core-annulus structures over the height of reefed line orifice. The simulation results fit well with the experiment results.