Abstract:Data for breath height diameter, stand height，number of individuals，standing biomass plant age we measured from 256 temporary plots and 24 permanent undisturbed plots of Pinus massoniana plantations on hilly land of north Fujian Each plot covered an area of 0.06-0.08 hm-2 Permanent plots were investigated for five times in the study. The original stand density was 3 000-4 500 trees aged from 8 to 34 with site index of 16 m．Self-thimting mode1 was based on the model for biomass of population growth, ie. dB/dt=rB[1-(B/K)θ] and by law of 3／2 self-thinning，from which the following model was dcduced：N＝｛[A(1+ce-ft)b]-p-[A(1+ce-ft0)b]-p+N0-p｝-1/p. This modeI can well imitate the actual population density observed，suggesting that it is a more accurate and applicable model．
