Based on 5 afforestation densities (1 m×1 m, 1.5 m×1.5 m, 2 m×1 m, 2 m×2 m and 2 m×3 m respectively), we determined the effect of stand density on the spatial distribution fine root biomass and provided theoretical supports for plantation management and operation in a 14yearold plantation of Pinus kesiya var. langbianensis in Puer City, Yunnan Province. The result showed that: (1) tree height and the diameter at breast height (DBH) increased with the decrease of stand density, while stand biomass increased with the increase of stand density. (2) The fine root biomass decreased with the development of stand density in the 14yearold P. kesiya var. langbianensis plantations, while the fine root biomass per single tree increased with the reduction of stand density. Meanwhile, the coarse and dead root biomass had no significant difference in five stand densities. (3) The fine root biomass mainly distributed in the soil surface, and 40.21 %-54.73 % of fine root biomass focused on 0-10 cm of soil depth. The fine root biomass indicated the trend with decreased accompanied by the increase of soil depth in the different stand densities. (4) With the increase of stand density, the proportion of fine root biomass showed firstly increase, then decrease in the soil upper layer, stand density and soil depth had significant effect on the fine root biomass. Tree individual size inequality had a negative influence on the fine root biomass, while fine root biomass per singe tree had significant negative influences on the stand density, individual size inequality, belowground biomass and basal area at the DBH, with the positive influences on the DBH and height.