Abstract: Car models were built by software CATIA.In consideration of the flow field characteristics of a car aerodynamics,three-dimensional incompressible Navier-Stokes equations and RNG(renormalization group) k-ε model were used in simulation.Second-order upwind difference scheme was applied to obtain the physical quantities of control pedal.The cooling air inlet of engine compartment was placed in the front of car,simulation on three different removal modes of cooling air was implemented to select a superior ventilation mode by comparing with aerodynamic characteristics of car.The flow inlet of cab was placed between the hood and windshield,simulation on three different removal modes of flow inside the cab was implemented to select a superior ventilation mode.Interior flow of engine compartment has greater impact on drag coefficient,interior flow of cab has greater impact on lift coefficient.