Abstract: According to satellite data,observational meteorology data station and monitoring data of PM₁₀ provided by Beijing Municipal Environmental Monitoring Center and through analysis of synoptic chart,the formative causations and the characters of the contaminative synoptic process which lasted from 1^st Nov.to 7^th Nov. in 2000 have been analyzed.The results showed that PM₁₀ has qaasi normal distribution during the research period that was composed of two completely different phases.The first phase (from 1^st Nov. to 3^rd Nov.) was brume pollution,the pollutants of which were sulfate and nitrate particulate formed by chemical reaction of SO₂ and NO₂,etc.The second phase (from 4^th Nov. to 7^th Nov.)was dust storm pollution,caused by loess,and floating dust produced by the upwind dust storm weather.Corresponding meteorological processes and synoptic forms during the two phases are different.During the first phase and before the sand storm broke out,the weather was controlled by homogeneous pressure field and with inversion structure of double layers and high relative humidity.During the second phase,the weather was dominated by northwest air stream existing foreside of anticyclone,the relative humidity has descended greatly,and the atmospheric drying degree is radically consistent from ground to upper air.