This paper simulated the heat transfer process of a cabin with air-conditioning cooling under natural exposure, and obtained the steady temperature distribution of the cabin thermal environment and the body. Some experiments were conducted to find out the transient change law of passenger compartment temperature with air-conditioning on/off. The simulation results show that the front cabin is cooler than the rear cabin, but the regional temperature differences on vertical direction is large. Large temperature difference is also observed on the human model. The experiment results agree well with the simulation ones, and it is found out that the air-conditioning cooling model can effectively reduce the temperature unevenness of the front cabin. And in the first 10 minutes of cooling the temperature changes rapidly, and after that only small temperature variation is observed.