The automotive HVAC system plays various roles such as car indoor heating, cooling and air quality control. This HVAC system consists of air-vents, ducts, heater, evaporator, HVAC module, etc. Recently, the research related with this is being performed through numerical analysis as well as experiments. A large amount of computation time is required when considering all parts of complicated HVAC system including an air-vent because the number of grid would be increased. Also, the working time will be increased if you perform the parametric analysis about the directions of an air-vent which decides an air discharge angle because CAD(modifying the geometry) and grid regeneration tasks are required. In this study, we removed the HVAC system including the air-vent from the computational domain and imposed the direction of the flow by using vector in order to shorten the working time according to the modification of the air-vent geometry. Also, it is expected that there will be a change in the car interior flow depending on consideration of air vent, so we performed various parametric study in order to set the flow without HVAC system to be the same flow considered the real geometry of air-vent.