Abstract: In order to research the source of hydrocarbon in ambient air.natural hydrocarbonernisions from dominant tree types in Beijing(poplar,willow,pine,cypress,etc)as well as lawnand paddy field(during the growing peak period of paddy)have been investigated using enclosuretechnique and chromatography analysis. It has been found that deciduous such as poplar,willowand Chinese scholartrees emit chiefly isoprene, coniferous(pine and cypress)emit usually ter-penes. The grass and paddy emit low-carbon hydrocarbon compounds. These research results aresimilar to those in some literatures.