Abstract: The methods in which different of space distribution stands for progress of time and the dimension analyses were used to study the biomass of four different secondary tropical forests in Xishuangbanna. The dynamic on the biomass of secondary tropical forests at the early stages of the secondary succession was analyzed in detail. The results show that the total biomass of four secondary tropical forests increased with the stand age. Total biomass in 5-year-stand, 10-year-stand, 14-year-stand and 22-year-stand were 41.932t· hm-2 , 52.116t·hm-2, 88.284t· hm-2 and 113.743t·hm-2 ,respectively.In the allocation of biomass in different layers in four stands, the biomass of tree layer was over 80% of the total. The biomass of shrub layer increased until 14-year old, then droped down, while the biomass of grass layers decreased and that of inter-layer increased with the stand age.Concerning different parts of plant in the four stands, the biomass of trunk, which occupies over 50% of the total, increased with the stand age, but those of branch, root and leaf decreased. The optimum regression models of different dominant plants and organs of the sample trees of tree layers in the four stands of secondary tropical forest were built.