In this study, the Fire Dynamics Simulator (FDS) numerical simulation method is adopted to analyze the influence of various smoke block board sizes, heat release rates (HRR) and exhaust velocities on the smoke entrainment near a mechanical exhaust vent. The results indicate that the smoke extraction performance of the board-coupled shaft is influenced by the coordination of the smoke block board layout, the heat release rate and exhaust velocity. Besides, the reasonable size of the board can effectively reduce the air entrainment and achieve the best smoke exhaust efficiency. When the board size is smaller than the exhaust vent size, there will be an inefficient exhaust smoke. When the board size is larger than the exhaust vent size, the exhaust smoke efficiency increases rapidly with the increase in the board size. In addition, the exhaust efficiency is insensitive to the HRR under the same board. However, the exhaust velocity exerts a significant effect on the layered stability and smoke extraction performance near the exhaust vent.