Aiming at the issue of low efficiency of nitrogen displacement of large packing box, the influencing factors of the two-dimensional model of packing box filled with nitrogen for gas displacement were analyzed by the Component Transport Model of Fluent. The results showed that the replacement rate of nitrogen gas increased with the increase of the filling speed，but the excessive filling speed led to the disorder of the gas in the packing box，which was unfavorable to the gas equilibrium discharge，and the diameter of the exhaust port had little influence on the increase of the replacement rate of nitrogen gas. The position of exhaust port had little effect on increasing the gas displacement rate，but lowering the position of exhaust port was beneficial to the smooth and uniform exhaust. Based on this result，the nitrogen displacement process of three-dimensional packaging box was analyzed. Compared with the actual situation，the results showed that the simulation calculation was effective and could be used as a theoretical reference for practical engineering application.