Abstract: The relationship between the damage level caused by Tomicus piniperda and the economic losses of Pinus yunnanensis was regularly observed on Fangwang forest farm and Jindian forest farm in Kunming and the forests at Dalongkou,Xiaolongkou,Xichong and Biaoluo in Yimen County.By statistical analysis, the controlindex of Tomicus piniperda was determined as follows:the mean insect hole was0.189/tree.the mean rate of withered trees was 0.52%.the mean rate of withered branchtops was 4.74%,and the mean rate of infested trees was 5.14%. By control testing in 473hm² of pinus yunnanensis forests at Dalongkou,Xiaolongkou, Xichong and Biaoluo,the damage level was already stabilized.The economic-threshold on Fangwang forestfarm was decided as 0.2151 holes/tree. By considering the actual situation of differenthrests, some flexible economic threshold was decided:when the density of insect holesreached 0.3338×CC÷CYEC(XP),the corresponding withered rate was 0.389+0.3667×CC(Y×EC×P),the mean rate of the withered branch tips was 5.5398+1.1301×CC÷(Y×EC×P),the mean rate ofinfested trees was 1.63+14.4821×CC÷(Y×EC×P), and thecontrol cost and the economic loss were the same so that control measures should betaken. The spatial distribution of Tomicus pinlperdaTomicus piniperda.