Abstract: The tree relative growth equations were established on the basis of measurement values of 30 sample trees using harvest method, which were used to estimate the forest community biomass. The result showed that the above-ground biomass of the typical community dominated by Platycarya longipes and Cyclobalanopsis glauca in Maolan Karst forest was 168.02t/hm2. It is ranked within the forest ecosystems of low biomass. The biomass variances of 3 different forest types distributed on mountain ridge, mountain slope and mountain valley in Maolan Karst region were investigated. The biomass components were analyzed according to life form, storey and species within tree stratum. The productive structures of some tree species as well as their reasons were also discussed.