The effect of traffic controlled on the air pollution in city was studied by micro pulse lidar (MPL). The optical characteristic of subaerial aerosol over Beijing was monitored continually with MPL in August of 2007. The system structure and technical parameters of MPL were presented and the data-processing method was discussed, the time-space distribution of aerosol extinction coefficients, heights of planetary boundary layer (PBL) and aerosol mass concentration were showed and compared with the results which were measured in the similar meteorologic condition during traffic uncontrolled. The results indicate that the aerosol mass concentration was falling, and the height of air pollution mass changed thin. All these proved that the program of traffic controlled improved the quality of city air. The experiment provide scientific groundwork and reference to the study of the air pollution.