Parked car ventilation reduces the cooling time of the front windshield, improves the efficiency of the dehumidification in the cabin and effectively improves the defrosting performance of the windshield. Based on the CFD method and the Realizable k–ε turbulence model, this paper studies the cooling of the front windshield and the dehumidification performance in the cabin. First, the simplified model test is used to verify the accuracy of the simulation method and to testify that the parking ventilation can prevent frost from building up on the inside of a window. Second, the parking ventilation process is simulated to obtain the relationship between ventilation parameters, cooling and dehumidification effects, and flow field structures. The results show that the rate of flow of defrosting airflow is the key factor in terms of the cooling effect of the front windshield compared with all the other ventilation parameters. In addition to the high rate of flow of defrosting airflow, deflecting upward the airflow from the dashboard vent which are fully opened benefits the mixing and discharging of airflow.