Abstract: In this paper, the root characteristics, the biomass allocation patterns of aboveground organs and root in different diameter classes of Pinus kesiya var. langbianensis plantation were studied. Biomass equations for various organs of P. kesiya var. langbianensis plantation were established based on independent variables including DBH and tree height. We aimed at providing a scientific basis for accurate measurement for carbon storage of the P. kesiya var. langbianensis plantation’s arborous layer. The length and specific root length (SRL) of coarse root, large root, medium root and small root increased but the SRL of fine root decreased with the increase of diameter class. The biomass proportion of medium root, small root and fine root decreased first and then increased with the increase of diameter class, while that of coarse root and large root increased first and then decreased. For the same diameter class, SRL of fine root was much higher than that of other roots. Biomass of various organ ranked as stem>branch>root>needle>cone, and the stem biomass accounted for >50% of the total biomass. Each organ biomass increased with the increase of diameter class, and aboveground biomass was significantly positively related with underground biomass. The individual aboveground biomass ranged from 2.23 to 324.95 kg and belowground biomass ranged from 0.52 to 41.80 kg. The biomass of root collar, taproot and lateral root increased with the increase of diameter class. Collar/taproot, collar/totalroot and lateralroot/taproot ratios were significantly positively related with DBH and tree height, and taproot/totalroot ratio had a significant negative correlation with DBH and tree height. AIC_NLR-AIC_LR values were larger than 2, showing that the linear equation was reasonable. The index of R²_adj was 0.661-0.992. The equations including tree height could improve model fitting performance and predicting precision of the biomass of the whole tree and organs except for cone.