Monthly mean NO2 concentrations in both urban and suburban areas of Beijing generally decreased in August from 2002 to 2008, with a decreasing rate of about 10% during the first five years and nearly 40% in 2008. Based on sensitivity studies with a Nested Air Quality Prediction Modeling System(NAQPM/IAP), quantitative assessments of the impacts of weather conditions and pollutant controlling measures on decreases in NO2 concentrations were made during Beijing Olympic Games in 2008. The impact of area and point emission controlling measures on NO2 concentrations was compared. The results indicates that pollutant controlling measures play a key role in decreases in NO2 concentrations during Beijing Olympic Games while the August weather condition in 2008 is more favorable for dispersion and scavenging of air pollutants compared with that in 2006. Area emission controlling measures are more effective than point emission controlling measures for decreases in NO2 concentrations.