The motion of granular wafers relative to its speed and the opening-size at choke point has been studied experimentally on a two-dimensional conveyer belt. The result shows that there is a critical speed vc when the opening-size d is fixed. The rate of flow Q increases linearly with the speed v, when v＜vc.The change of the Q-v curve occurs at the speed of vc.The critical speed vc is dependent on the opening-size d. The interaction between the granular wafers is changed when altering the speed or the opening-size at the choke point, and affects the motion of granular flow.