This paper analyzes difference between current tunnel ventilation calculation method and advanced one which considers effects of polluted air recirculation near tunnel portals. For the calculation, CFD(Computational fluid dynamics) technique was utilized. From the result, it was found that 4.38% more fresh air is required when there is polluted air recirculation near tunnel portal areas. Hence, it is recommanded that the consideration of polluted air recirculation should be made when deciding the ventilation requirements for tunnel.