The aim of this work was to research the force of granular material in door-form feeding mechanism on the material door, so as to choose appropriate drive mechanism. After reasonable simplification of the feeding mechanism structure, PFC3D based on DEM was used to calculate the force on material door exerted by granular material when the material door was completely closed, then the material door and its associated mechanism were simplified into bar mechanism, and the required driving force in several key positions of the material door. The results showed that the vertical direction force suffered by the material door was always smaller than the material gravity, and this phenomenon became more significant with increasing material height. The positive pressure and tangential static friction of the door suffered from material increased linearly with the increase of material height, then increased nonlinearly, and final it tended to approach a limit value. This change had a relationship with the structure of hopper. When the door was fully closed, the oscillating lever force required to open the door was about 115N. At the accurate feeding position, the limiting lever force required to maintain the accurate feeding was about 553N. When designing door-form feeder mechanism, the force suffered by the material door was only needed to be calculated at a certain material height, with further increase of material height the force of material door suffered from material kept almost constant. In the feeding mechanism used in this paper, the cylinder could provide sufficient driving force to ensure the proper functioning of the mechanism.