Populus davidianaand Pinus tabulaeformis Carr.are two important tree species in western Shanxi Province.Biomass of each component and above and below-ground biomass of Populus davidianaand Pinus tabulaeformis Carr.were obtained by harvesting 40trees with various diameters at breast height(DBH),and furthermore,their allocation patterns were analyzed.Allometric models for each component(leaves,branch,stem,root,aboveground and the whole tree)of Populus davidiana and Pinus tabulaeformis Carr.were then developedbased on independent variables including DBH,tree height(H),trees factor(D2 H),average crown width(CW),and crown length(CL),and the best fitting models were identified.The results showed that relativeproportions of leaves,branch,stem and root to the total tree biomass were 3.42%,11.23%,64.30%and21.06%for Populus davidiana,and 13.44%,19.86%,47.52% and 19.18%for Pinus tabulaeformisCarr.,respectively.The ratio of aboveground biomass and belowground biomass were 3.32:1and 3.99:1for Populus davidiana and Pinus tabulaeformis Carr.,respectively.The two variables were correlated linearly forboth Populus davidiana and Pinus tabulaeformis Carr.(p<0.001).The best fitting models of two species wereCAR models.The allometric models explained more than 92%of the variance in the data,biomass allometricmodels based on DBH explained more than 90%,while leaves biomass allometric model explained more than83%.Tree height should not be used alone to predict the biomass of each component.Considering the variance explainability and the practical need,it can be concluded that DBH is a reliable predictor for estimatingthe biomass of each component for both Populus davidiana and Pinus tabulaeformis Carr.