Abstract: Raw grain generally refers to the unprocessed cereal in agricultural production. In general, the raw grain can be packed from autumn after harvested in northern China. A bag opening mechanism has been one of the most important components in raw grain packing machines. Different cylinders can be usually utilized to drive the bag clamping and opening mechanisms. The performance of this mechanism directly dominates the quality of raw grain packaging. However, the slow action or even failure of pneumatic parts can result in the reduced synchronization and efficiency of machines, due to the condensation at low temperature and the environment of heavy dust. In this study, a bag opening mechanism driven by a cam that moved synchronously with the bag clamping mechanism was designed. The synchronous actions of bag opening, clamping, and resetting were also realized using one motor to drive the planar six-bar-linkage. A systematic investigation was then made to clarify the working requirements, structural composition, and working principle of the bag clamping and opening mechanisms. A sinusoidal acceleration motion was selected as the movement rule for the cam driven bag opening mechanism. The geometric coordinate transformation and the vector method were established for the parameter equation of the cam working profile and the pressure angle solution of the spatial cam mechanism. A single factor test was also carried out to evaluate the performance of the cam driven bag opening mechanism using the influencing factors of the pressure angle. An optimal combination was achieved, where the radius of bag opening rod was 6 mm, the angular displacement of bag opening rod was 4.5°, the swing distance of the contacting point was 120 mm, the initial positional angle of the contacting point was -180°, and the positional angle of the contacting point was -170°. A linear fitting was obtained between the angular displacement of bag opening rod and the positional angle of the contacting point. The maximum pressure angle of 23° was less than the allowable pressure angle. Finally, the specific parameters were determined for the movement of cam driven bag opening mechanism, the cam working profile, and the relational expression of the pressure angle. A 3D model was constructed for the cam driven bag opening mechanism. The motion of the cam driven bag opening mechanism was also simulated using ADAMS platform. The theoretical calculation and simulation show that the bag opening movement was basically the same, fully meeting the actual requirements of mechanism. In addition, the physical prototype was manufactured for the bag opening mechanism. A comparative test was performed on the bag clamping and opening mechanisms that driven by cylinders and motor. Consequently, the productivity of 10 bags/min was obtained on the motor-driven type, which was much higher than the cylinder-driven one. The feasibility and accuracy of the cam driven bag opening mechanism were verified to fully meet the requirements of packaging process. This finding can also provide a new idea and theoretical analysis to design the raw grain packing machine in the cold regions.