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One year (from June 2009 to May 2010) measurements of PM2.5,aerosol absorption coefficient and scattering coefficient were analysed at an urban site in Beijing.Annual averages of PM2.5,absorption coefficient,scattering coefficient,single scattering albedo,mass absorption efficiency and scattering efficiency were 67.39±66.23 μg m-3,63.73±62.06 Mm-1 and 360.45±404.96 Mm-1,0.82,0.78 m2 g-1 and 5.55 m2 g-1,respectively.With maximum during the night and minimum in the afternoon,absorption coefficient and scattering coefficient showed the same diurnal characteristics while SSA displayed contrary tendency.Wind reduced the impact of the aerosol optical properties on atmospheric visibility,but sometimes airflow derived from the southeast of Beijing could cause absorption coefficient and scattering coefficient increase in the summer and autumn.It was the accumulation of pollutants that resulting in the rise of absorption coefficient and scattering coefficient and the visibility deterioration in summer,autumn and winter while in spring,the airflows from the dust sources elevated the particulate concentrations several times,but had limited effect on absorption coefficient and scattering coefficient.The frequencies of haze in autumn was higher than other seasons and visibility exponentially decayed with increasing PM2.5 concentration,which should be controlled lower than 64 μg m-3 to preserve the visibility more than 10 km.