Aimed to study the dynamics of the biomass and allocation of the Pinus massoniana plantations with different stand ages (5a,15a,21a,32a,60a) in Guangxi,South of China,we established fifteen plots,each with a size of 20 m×50 m,at different sites.By using the investigation data of 21 Pinus massoniana trees with different ages and diameters at breast height,the regression model of the biomass relating with D (diameter at breast height,1.3 m) was established.And other biomass components were sampled in different quadrates in fifteen 1 000 m² research plots:shrubs (three 4 m² quadrats),herbs (three 1 m² quadrats) and litterfall (three 1 m² quadrates).This method applied to estimate the biomass and allocation characteristics of biomass with stand age.Results showed that:(1)The biomass of the stands increased with stand age,being 15.03 Mg/hm² in 5a stand,125.93 Mg/hm² in 15a stand,183.51 Mg/hm² in 21a stand,191.53 Mg/hm² in 32a stand,405.31 Mg/hm² in 60a stand,and living biomass and litter made up 75.01%~94.19%,0.86%~24.99%,respectively.(2)Most biomass (90.20%~98.35%) of Pinus massoniana plantation was concentrated in the tree layer,and grown with stand age,next was the litter layer,made up 0.86% to 24.99%;Shrub and herb biomass contributed small,made up 0.47% to 34.85%,0.32% to 27.00%,respectively,and decreased with stand age.(3)The biomass of the trunk occupied the greatest proportion of tree layer,made up 49.93% to 83.10%,increased with stand age;Root had a relatively stable biomass,accounted 6.97% to 12.82%;Branches and leaves made up 11.75% to 14.83%,1.33% to 23.65%,decreased with stand age.The biomass allocations of shrub were branch>leave,except root>branch>leaves in young (5a) forest.The above-ground biomass was higher than under-ground biomass in middle-aged (15a) and near mature (21a) forest,but opposite to that of other stands.(4)The litter biomass ranged from 3.48 to 6.68 Mg/hm²,the law was not obvious.(5)Biomass of all tree organs and stand of Pinus massoniana plantation showed a good growth model.Compared with other forest,the total biomass of 32a Pinus massoniana plantation was higher than that of the Phoebe bourmei Plantation,but lower than that of tropical rainforests,and it is the fast growing forest tree species with higher photosynthesis efficiency and potential carbon fixation.