Abstract: To estimate the biomass of Pinus yunnanensis Franch. Seedlings, the estimation models of biomass of different organs and individual plant for six different classes of P. yunnanensis seedlings were constructed after the determination of the proper independent variables, which were ground diameter (D), height (H), ground diameter and height (DH) or the square of the diameter multiplied by height (D²H). The optimal model was selected according to the largest correlation coefficient (R), the smallest standard error of estimates (SEE) and significance level (P＜0.05). The results showed that the optimal biomass models for different classes of P. yunnanensis seedlings were mostly power function, quadratic and cubic equations, and the optimal variable was D²H in most cases. The optimal variable of class Ⅰ and Ⅵ was D²H, it usually was DH for class Ⅱ and Ⅲ, DH and D²H for class Ⅳ, and D and D²H for class Ⅴ. All the three estimation models displayed good and precise estimation of the seedlings biomass, yet for different classes the independent variables and optimal equations were not completely identical. Therefore, it was impossible to construct a relatively uniform equation for the six different classes of seedlings with same variables.