Abstract: Based on density theory of plant growth and related biological hypothesis, a theoretical model describing the whole change process of plant population density was derived, i.e. N=exp(aln²v+blnv+c), where N and v represent population density and mean volume of a plant, and a,b,c are parameters. Thereby, the authors proposed a self-thinning mechanism model which can be used in different sites and different growth stages of Chinese fir plantation, the model was described as N=exp(5.895932H^0.01351034 - 0.9225263H^-0.002829299lnv -0.1148481H^-0.01018257ln²v).The simulating result showed that the mechanism model fitted the data observed from Chinese fir plantation very well. Therefore it is very useful in practice, which will provide a scientific basis for sustainable management of Chinese fir plantation.

Key words: Chinese fir plantation, Self-thinning