Abstract: An integrated MM5,Models-3/CMAQ modeling system was applied to study SO₂a air quality in Beijing and its surrounding regions by the effects of power plant emissions from Hebei,Tianjin,Shanxi and Inner mongolia.The result of simulation indicated that high SO₂a concentration was appeared in regions with high density of power plants and high emissions magnitude.SO₂a concentration in Beijing was decreased from south to north,with monthly concentration of 7.63 and 7.13 μg/m³ in January,monthly concentration of 5.54 and 5.37 μg/m³ in April,monthly concentration of 3.02、3.68 μg/m³ in July,monthly concentration of 7.49、7.53 μg/m³ in October,and annual concentration of 5.92 and 5.93 μg/m³ in 2005,for urban and entire city of Beijing,respectively.The maximal daily concentrations of urban and entire city of Beijing were 30.1 and 19.1 μg/m³ in January,which were 20.1% and 12.7% of the class Ⅱ national air quality standard.Power plant emissions in north China induce or enhance air pollution in Beijing,which should not be neglected.