The airflow field in cartons of the pressure-difference pre-cooling litchi was simulated by using Fluent software based on standard model and SIMPLE algorithm. The fitting equation of the relationship about length of cartoon and static pressure in cartoon was gotten with the fitting accuracy 0.817, which was verified by experiment. The experiment and simulation shows that the law between the internal pressure and length of the cartoon is positive correlation, and the pressure of air entrance is high, the pressure of air outlet is low.