The concentrations and the variation characteristics of the main pollutants including SO2, NO2, O3 and PM10 during Beijing Olympic Games were investigated based on data collected during the period from June 20th to September 22nd, 2008, at four locations in Beijing: Institute of Remote Sensing Applications, Yungang Town, Yanshan Petrochemical and Capital Airport. PM[EQUATION] is reported to be the major pollutant. The analysis shows a significant higher level of PM[EQUATION] in urban site than in rural. A ratio difference of 50% for PM[EQUATION] between rural and urban site in the first period (from July 1st to 19th and from July 20th to August 24th) was observed, which decreased to about 25% during the second period (from August 8th to 24th and from September 6th to 17th). The difference on diurnal variation of PM[EQUATION] mainly appeared during 01:00[EQUATION]11:00. The concentrations of primary pollutant SO[EQUATION] and NO[EQUATION] were below the Grade-II standards. With the implementation of mitigation measures, a decrease of the above two pollutants exceeded 14%. The results also showed that diurnal variation of NO[EQUATION] had a very clear cycle with two peaks in most stations, but only the case for SO[EQUATION] in Yanshan Petrochemical and Yungang Town stations. As the indicator of photochemical smog O[EQUATION] exhibited an obvious diurnal variation with high levels during daytime and low levels in nighttime. Two peaks of O[EQUATION] diurnal variation during daytime were observed in Yanshan Petrochemical and Yungang Town stations. Based on the statistical data the levels of O[EQUATION] increased at the early stage of reduction of pollutant emissions (before July 20th) and then continuous declined. The ratios of the maximum to minimum for O[EQUATION] showed a downward trend after June by analyzing the different diurnal patterns. Each pollutant of the above revealed a remarkable drop during the period from August 8th to 24th, 2008. Comparing the statistical data obtained from July 1st to 19th, with those obtained from July 20th to August 24th in 2008, SO[EQUATION], NO[EQUATION], O[EQUATION] and PM[EQUATION] decreases by 14%[EQUATION]33%, 15%[EQUATION]61%, 2.5%[EQUATION]14% and 10%[EQUATION]12% respectively.