Abstract: The purpose of this study was to research for a available method on the population dynamica and outbreak forecast of the pine caterpillar (Dendrolimus punctatus Walker).Based on the results of the prevenient studies, we made an integrated analysis on the relationships between population dynamics and the enviromental conditions which include habitat, climate, food and natural enemy factors, etc.The different conditions of injury of the host plant (Pinus massoniana Lamb.) intimately influence the gradation, mortality, fecundity, migration and parastic percentage of the present and subsequent generations. The results of all these influences were reflected in the reptoductive capacity.The mathematical model of the population dynamics is put foward as:Where N_t=population density at t generationsN₀=prime population densitye^k=reproductive rate from generation to generationt=number of generationsx=survival degree of pine needlesGenerally speaking, the precipitation in May (X₁) and the average temperature in Febuary (X₂) exerted a decisive effect on the occurence of outbreak in Jiangxi province. In addition, the back-cold in early spring, rainstorm and the long-lasting dry climate are the limited factors to the population dynamics. The criterion function Y=0.048X₁+0.341X₂ and the critical value Y_c=4.240.