The environment factors such as solar radiation, air temperature and velocity have considerable effects on thermal comfort of the passenger as well as vehicle air-conditioning system. This study is focused on the calculation of vehicle external heat load of the car body components. The external heat load distribution for sedan is calculated using numerical simulation with a virtual environment grid system. The thermal physical property of the cabin wall is estimated by simplifying complex geometry to uniform laminate configuration. Combine refrigerating and air-conditioning theory and conjugated heat transfer between turbulent flow field and car body components, the transient 3-D simulation of the cooling process are performed to predict the flow field and temperature distribution. The numerical results are in good agreement with the experiment measurements.