Aerosol samples were collected continuously by a step sampler with a 2hour time step during 30 September－6 October 2001 at meteorological tower at the height of 8 m in Beijing. Chemical composition of aerosol samples was analyzed by using PIXE method. The results showed that the diurnal variations of element concentrations were remarkable, and higher pollutant concentrations often occurred in the morning and midnight. Enrichment factors of S, Pb, Cl, Zn in atmospheric aerosol in Beijing which had a close relationship with the human activities were very high. Factor analysis for element concentrations further indicated that main sources affecting atmospheric aerosol concentrations in Beijing were soil matters, coal combustion, industry dust and vehicle emission.