Abstract: The assessment of average stem density of Pinus kesiya var.langbianensis was conducted in order to measure stem biomass of large sized trees.The average stem density of Pinus kesiya var.langbianensis was evaluated under three hypotheses by the regular regression model for density assessment.The differences in the stem density among different positions on the stem and among varied age groups were verified by dummy variable method on the basis of selecting the best estimation method through comparison.The results showed: The best estimation of the stem density of Pinus kesiya var.langbianensis was obtained by method Ⅲ,by which the influence of heteroscedasticity could be eliminated.Method Ⅰwas the best one for bark density estimation.There were no significant differences in the stem density among different positions on the stem,but there were significant differences in bark density among samples taken from the upper and middle,upper and lower parts of the trunk,although the bark density of the middle part of the trunk was not significantly different from the lower part.There were no significant differences in either timber or bark density between middle aged and premature plantations.It was proposed that the uniform value of the average stem density could be applied to estimate the dry weight of Pinus kesiya var.langbianensis stems by volume density estimation method.