An apparatus for preparing granular polysilicon comprises a reactor tube, a reactor shell, an internal heater, and components for controlling pressure, supplying a fluidizing gas and a reaction gas, discharging gas, and discharging particles. The reactor tube is associated with an inner space comprising an inner zone that contains a bed of silicon particles and is the site at which silicon deposition occurs. The inner zone comprises a heating zone and a reaction zone. The fluidizing gas supplying component supplies a fluidizing gas for fluidizing the bed of silicon particles to a bottom of the heating zone. The apparatus can minimize the problems occurring during the heating of silicon particles at high temperature for silicon deposition on the surface of the silicon particles.