Ecological greening is an important way of highway greening.Community stability and species diversity are the two essential characteristics of highway ecological greening.By taking Populus tomentosa communities in the Shunyi section of Shunping Road (S305) , Beijing , as a research object and applying WinSCANOPY produced by Regent Instrument of Canada in taking photos , light environment over and under the canopy and community structure characteristic indexes , such as photosynthetic photon quanta flux density (PPFD) , gap fraction , leaf area index(LAI) , and mean leaf angle(MLA) , are analyzed by data analysis and field investigation.Results show that the gap fraction of Populus tomentosa communities decreases with the diameter at breast hight(DBH)increasing and MLA decreases with the DBH increasing.Although LAI fluctuates in some degree , it also presents an ascending tendency.The study provides a basic analysis and a reference for highway ecological greening to establish a stable plant species diversity and a multi-layer structure.