An integrated air quality model that combines a CFD model and multi-room pollutant transport model has been developed to study the effect of traffic pollution on indoor air quality of a multi-room building located in close proximity to busy roads. The CFD model conducts the large eddy simulation of the three-dimensional turbulent flows and pollutant transport processes in outdoor, whereas the multi-room pollutant transport model performs zonal airflow and pollutant transport in indoor. The integrated model is verified with available field measurement of traffic-induced CO concentrations. Twelve scenarios of numerical experiments for various configurations of window openness are carried out to study the effects of the air change rate and the outdoor pollutant dispersion on indoor air quality. It is concluded that the windward side opening is a significant factor contributing to indoor air quality. Using air inlets on the sideward and leeward envelopes simultaneously can effectively lower the daily mean and peak indoor levels of traffic pollutants and maintain a desirable air change rate.