An vertical organic waste fermentation treatment system has been developed, which composed of main agitator, feeding device, ventilation system, transmission, and discharge part. The organic waste was fed through the feeding device as well as the appropriate bacteria, and then mixed by the main agitator. The ventilation system provided adequate fresh air to ensure the organic waste fermenting completely. The transmission transmitted power to the whole system. When the fermentation is finished, the organic waste was discharged by the discharge part. Resistance of the main agitator was studied during the fermentation process under normal condition. The mathematical model of the agitator was established to simulate and analyze the movement of the material in the cylinder and the force on the agitator by discrete element soft of EDEM. The results show that the average torque on the main agitator was 84 927.6 N?m obtained by simulation, which slightly larger than the value of 86 549 N?m from theoretical calculation. It is found that the simulation by EDEM is consistency with theoretical calculation.