Objective: To analyze the effect of apples of different fruit diameters on differential pressure precooling under the same box. Methods: Based on the spherical analogy model and heat transfer theory, the CFD unsteady SST k-ω turbulence model was used to numerically simulate the differential pressure precooling of apples with different air supply air speed, temperature, box opening size and fruit diameter, and three different working conditions were selected for accuracy. The simulation scheme of mixed orthogonal test was used to discuss the effects of different factors and different fruit diameters on the cooling rate and pre-cooling uniformity. Results: The lower of the air supply temperature was, the faster the wind speed was, the smaller of the apple diameter was, and the faster of the cooling rate it was. The higher of the supply air temperature was, the faster the wind speed was, the larger of the opening was, and the better of the uniformity of precooling it was. Based on the comparison of orthogonal test results, the effect of fruit diameter on differential pressure precooling was significant. Conclusion: Apple fruit size has the greatest influence on the cooling rate and uniformity of pre-cooling, and reasonable packaging and stacking methods need to be adopted for apples with different fruit diameters.