Abstract:Based on Zhang's model for Populus tremula var. davidiana and Pinus yunnanensis forests, a mathematical model of forest population density regulation during self-thinning is presented. The new model was tested using the Algorithms of Contraction-Expansion. The results showed that the new model could fit the observed data very Well. Algorithm of Contraction-Expansion used to optimize nonlinear equation is rational, which will enrich the research method in this field. The new model in the study of density regulation 1aw in Cunninghamia lanceotata forest is sarisfactory and can provide usefu1 information for the management of Cunninghamia lanceolata forest．