The work aims to make the cold air distribution of refrigerated truck more uniform during transportation and improve the cooling effect on goods. A cold air guide system was designed for refrigerated truck, and its three-dimensional geometric model and thermodynamic model during refrigeration were established. The changes of cold air flow direction and temperature field in the compartment with time during the transportation of apples were analyzed by means of calculation and simulation. The effects of key parameters such as pore diameter, pore interval, guide groove size, return air duct width and inlet wind speed on the cooling effect during the transportation were analyzed. Through the analysis results, the key dimensions of the cold air guide system were determined. It was found that the designed cold air guide system could reduce the maximum goods temperature by 5.9 K during transportation, and the width of return air duct should be about 150 mm. The designed cold air guide system can effectively improve the cooling effect, and the relevant methods can provide a certain reference for the design of refrigerated truck.