Abstract: In view of two underground traffic tunnels with longitudinal ventilation system in Beijing, methods of combined with full-scale tests and numerical simulations are used to research the ventilation status.The ventilation ability of an axial fan and jet fans, and the settings of boundary conditions in numerical simulations are investigated.From test and simulation results, it is found that equipping diversion shutter at the air opening of axial fan can enhance its effect of air supply to tunnel downstream, and the diversion shutter can be modeled by two vertical bevel faces at the edge of the air opening.Furthermore, the jet fan is suggested to be applied with pressure boundary condition.