Taking Qianjiang shield tunnel as the research object and based on the CFD simulation method, a large eddy simulation analysis software FDS is adopted to simulate and analyze the effect of exhaust rate on fire smoke control under the condition of the same heat release rate of 50MW and exhaust ports in a road tunnel. Ten different exhaust rates are simulated under the mode of bidirectional equilibrium smoke extraction. Comparative analysis are made on smoke flow velocity in exhaust ports, temperature at exhaust ports and exhaust fans, smoke exhaust efficiency, visibility distributions at two meters high of road, and smoke spread distance, when smoke exhaust rates are different. The results show that different smoke exhaust rates have great influence on smoke exhaust effect. The simulation results show that smoke flow velocities in exhaust ports are less than 10m/s, temperature at exhaust fans are less than 280℃, and visibility distributions at two meters high of road are more than 10m, which satisfy requirements of the design code. When the smoke exhaust rate are greater than or equal to 190m³/s, the temperature at exhaust ports is less than 280℃, smoke exhaust efficiency could reach at 100% and fire smoke is limited in the section of the opened exhaust ports. It is indicated that a quite good smoke control effect could be achieved. The results could provide some reference to design institutes for selecting exhaust fan.