This paper is aimed at studying changing trend of each performance parameter of a certain type of fan in the airliner ventilation system under the condition of variable flow rate. The parameters of fan efficiency, pressure rise, power, static pressure distribution on blade surface and the vortex structure in flow field were obtained by CFX numerical simulation. The calculation and analysis show that the total pressure efficiency increases with the increase of flow rate in a certain range, and the efficiency decreases sharply when the flow rate reaches a certain value. In addition, the change of flow rate leads to the change of static pressure on the blade surface and aerodynamic force on the fan. At low flow rate, the aerodynamic force on the impeller has a lowest point. The vortex structure in the flow field also varies with the flow rate in the give range, which is mainly due to the change of the attack angle caused by the flow rate.