Abstract: According to the measurement of the above-ground biomass of tropical mountain rain forests (original and regenerative forests) in Jianfengling, Hainan Island, the biomass of the two communities are up to 645.2 and 272.9t/ha(including litter biomass), the tree biomass are 96.9% and 94.0% of the totals, and the LAI values are as high as 16.70 and 9.07, respectively. Although the under-growth, liana, eiyphyte and parastic plants have high diversity, the biomass are less than 5% of the total. Comparision study show the original and regenerative forests have obvious differences in the total biomass, the distribution of the biomass in community layers and tree DBH classes. The regenerative forest dominated with Castanopsis fissa has higher productivity in the early stage. A 26-year-old regenerative forest’s average annual net biomass accumulation is up to 9. 8658 t/ha·a, which is close to that of the tropical plantations with middle-level management, and is one and a half times of that of the original mountain rain forest in Jianfengling.