Abstract: It is demonstrated that the voidages of the dense bed and its freeboard in the circulating fluidized bed are determined by the circulating rate of particle and the dense bed hight is controlled by the pressure balance around the particle circulating line affected by the hold-up of the particle in the downcommer and the pressure drop of the pneumatic valve.When the pressure drop of the pneumatic valve is too large or the hold-up of the particle in the downcommer is not enough, the dense bed disappears and whole bed is maintained dilute bed where the voidage has the same Value as that in the freeboard. Even when gas velocity is increased to 5m/s, definite trasition can not be observed from the turbulent flu-idization to other regimes of fluidization.