The experiment was carried out in the pine plantation of Pinus massonis and Pinus .elliottii in which the Massonis Pine Caterpillar (Dendrolintus punctotus Walker) has four generations per year. By simulating the damage caused by the Massonis Pine Caterpillar by articial defoliation of the pine tree and using the design of stochastic group, we got the following; 1) There is no great difference in the amount of needles eaten by each larva in four generations. 2) The model was constructed to estimate the amount of pine needles and percentage of wood volume losses by using the easy measurement. 3) Economic threshold of controlling the Massonis Pine Caterpillar were constructed.