In order to improve and enhance the cooling performance of the refrigerated trucks, a mathematical model of cooling process was established in a refrigerated compartment based on dynamic thermal equilibrium theory, by considering heat transfer of the external sol-air temperature through the compartment structure, air and water vapor leakage, and respiratory heat of goods within the refrigerated compartment. The correctness of mathematical model was proved by test. The test results showed that the air temperature decreased exponentially with time during the cooling process of air in refrigerated compartment. The cooling time increased when the thickness of compartment insulation material or cooling capacity of refrigeration system was reduced, or the thermal conductivity of compartment insulation material, solar radiation absorption coefficient of the compartment external surface, vehicle speed, leakage ratio of the compartment, respiratory heat of goods were increased. On the contrary, cooling time would decrease. The thermal conductivity of compartment insulation material, cooling capacity of refrigeration system, and respiratory heat of goods were thought to be the most influential factors. Besides, when the thermal conductivity increased 0.001 W/(m·K), the thickness of compartment insulation material would be required to increase 5 mm on the insulation capacity. The cooling time kept basically unchanged when vehicle speed in the range of 0~40km/h. However, the cooling time would be significantly extended along with the vehicle speed increase in the range of 40~80 km/h. The cooling time was not influenced by the air velocity within refrigerated compartment. 