Abstract: The middle-mountain moist evergreen broadleaved forest is the major forest type in the vertical vegetation zone of subtropical mountains. Its typical representative is the forests in Ailao Mountain, dominated by Lithocarpus xylocarpus, L. chintungensis and Castanopsis wattii. The biomass and mean annual net accumulation for the pre-matured and the matured or over-matured forest communities were estimated through harvesting and correlation: The results show that the biomass was 508.57t·hm-2 and 293.04t·hm-2 in the prematured and the matured or over-matured forests, respectively. Mean annual net accumulation was 12.1051 tons·hm-2·a-1 and 7.7443 t·hm-2·a-1, respectively. The causes for the differences were also analyzed. The leaf area index (LAI) of the two forest stands were 10.04 and 8.96, respectively. The regression models by which the biomass of different organs of dominant tree species in the community was estimated were established. The status of construcrive species in the communities was also explained in the light of biomass production.