Abstract: To predict biomass of forest stand quickly and accurately, Cinnamamun cassia of Fangcheng was studied to establish the biomass model of trunks, barks, leaves and branches based on linear and nonlinear relations, and the effects of different densities of Cinnamamun cassia plantation on biomass of each organ and diameter classes was analyzed. The results showed that, the correlation coefficient of the optimal model of each organ had reached over 0.93, the optimal model was applied to estimating the biomass of each organ under the 4 densities, and the results were same as: trunk> branch> bark> leaves. The total biomass of the above ground showed that: density II> CK> densityⅠ> density Ⅲ, and density II (2400 plants /hm2) was the best density of the biomass of big-diameter timber in the Cinnamamun cassia plantation.