This paper makes a calculation of the smoke evacuation volume in a certain Olympic gymnasium by using the smoke control formula from NFPA92B,  and makes an optimization design of the smoke evacuation and ventilation system by using the Computational Fluid Dynamics (CFD) stimulation software.  It also discusses the inner relationship among the mechanical smoke evacuation,  the mechanical ventilation and natural ventilation as well as the influence of the mechanical ventilation volume on the smoke evacuation system in the Olympic gymnasium,  which provides the theoretical basis for the optimization design of the smoke evacuation and ventilation system in the Olympic gymnasium.