Abstract: The masson pine Pinus massoniana in the Sartshiliuqu Forest Farm is frequently and severely infested by the pine caterpillar Dendrolimus punctatus．The pest has three-four generations a year，chiefly three generations．The outbreak of the pest has taken place every two years since 1970s．For the last 12 years，after closing the masson pine forest，the forest has the ability to Stalld severe infes rations，while the masson pine forest of the eighbourhood was seriously damaged．It is proved that the closed forest has the advantages for less investment and good results in the control of the pest．As a result of closing the forest，the species of the undergrowth increase and the coverage rises．The community of the masson pine forest is then fundamentally changed．Moreover，the nature enemies，both species and populations of the masson pine eaterpillar apparently increase in the closed forest compared with the unclosed one．Thus closing the forest can improved the self-regaintion and natural control functions of the masson pine forest and obviously restrain the massion pine caterpillar rampaging．To close the forest，is therefor，the basic measure for the control of the pest．The 1000 ha．masson pine forest has been closed for 12 years，the outbreak of the pest does not occurr；thus。The control COSt has been cut down，the growing Stook has increased．