Abstract: In order to study the structural feature of the atmospheric boundary layer (ABL) over Beijing and the aerosol extinction characteristic in it, ABL over Beijing was observed with a potable Mie LIDAR in the summer of 2004. The vertical distribution of extinction properties and the height of ABL over the observation site were inverted. And the influences induced by meteorological conditions and human activities on the ABL structure were analyzed. The data indicates that the variation of ABL over Beijing in the daytime in summer is obvious. With meteorological parameters, the detected data of ABL heights and aerosol optical depth are presented and discussed. The research result shows that the ABL height is always less than 1.8km, its average height is 0.68km and the aerosol optical depths within 3km are about 0.3.