This invention belongs to the field of biomass energy utilization at the large scale. A material stirring device for a biomass bin includes a transmission mechanism, a main stirring mechanism, and an auxiliary stirring mechanism. The main stirring mechanism includes a cylinder connected to the transmission mechanism. The outer wall of the cylinder is provided with a hollow stirring rod. The auxiliary stirring mechanism includes a rotating shaft vertically penetrating through the hollow stirring rod. Both ends of the rotating shaft are provided with stirring blades and the rotating shaft is connected to the transmission mechanism. That the stirring device is easily damaged due to too high density of the biomass material is overcome through the automatic conversion adjustment of the main and auxiliary stirring mechanisms. The continuous discharge efficiency of the biomass bin is improved by the organic integration of over and partial stirring.