Abstract:This paper was written on the basis of the investigation of biomass of the mountainous humid evergreen broad-leaf forest in Ailao mountains, Yunnan, at April-May, 1982. This paper, with the Lithocarpus xylocarpus forest as its main object, is a preliminary study to make use of the harvest method for the evergreen broad-leaf forest ecosystems biomass in subtropical region. The authors give much emphasis discussed and analysed the problem on the community biomass, biomass of every structural layer and the essential species of community as well as the vertica1 distribution of root systems and the relationship of above ground parts and root systems etc. All these can be used as the reference of some departments and units concerned.