Abstract: The fatal factors of the winter generation pine-moth, D. punctalus Walker were observed on Chang Le Forest Farm of Zhejiang Province during 1979?982. The results are as follows. The larval stage has the highest death rate, mainly in the first and fourth larval stadiums, when the death rates are 30.4% and 39.3% respectively. It is caused by climatic conditions, i. e. changes of wind, rainfall and temperature. The main fatal factor for pine-moth D. punctatus walker at later larval stadiums is the predation of birds, particularly when the degree of density is low. Since Slash pine (pinus elliottii) has a rather high resistance to pine-moth, the death rate in the early larval stadiums is high and the unmber of female wackers and the quantity of eggs are reduced.