Abstract: Pollution property of particulates in the air and its affecting factors at the traffic crossing in Beijing were studied. Particulates samples of different sizes were collected at one of the major traffic crossings, Chongwenmen crossing, in June 2000. The mass concentration, ion concentration and element mass concentration in the particulates were measured. The flux of vehicles through the crossing during sampling was also investigated. Results showed that the pollution of particulates in the air was most serious on June 5. Especially at 0:10—3:50 on June 6, the mass concentration of PM_2.5 was the highest. There was not obvious relationship between the pollution level of particulates in Chongwenmen crossing and the flux of vehicle. The particulates from traffic were the major factor affecting the pollution level at the traffic crossing. The elements such as Al, Ca, Fe and Mg were mainly from the raised dust carried by vehicles and Cu and Pb were mainly emitted from vehicles. The research direction and technology route in the future were also pointed out.