Abstract:The masson pine caterpiller (Dendrolimus punctatus Walker) is the most important pest of the massin pine, Pinus massoniana, in our country. It is widely distributed in southern of China. In the pest, the insecticides such as BHC, DDT, Trichlofon etc. was frequently used in its control. Nowaday, the pyrethroids (e. g. Decamethrin and Fenvalerate etc.) have been used in many places to replace the Chlorinated hydrocarbon insecticides and the synthetic organic pesticides. However, owing to the abuse of insecticides, the problem of resistance is becoming a serious matter.The results of the laboratory tests showed that, in Lixai, Jimhua-Liging, Vanlin, Juzhou-Hangpu, Juzhou-Hengluzhu, Jinhua-Gufang province etc., the resistance to the Trichlorfon of the insect population had increased by21. 45, 26. 07, 26. 38, 27. 60, 27. 98, 55. 28 times compared with that of the insect population in Rongkang province (Table 2). In Jinyin-Chenbe, Rongcan-pidin, the resistence to the Decamethroin of the insect population had increased by 40.38, 49.40 times campared with that of the insect population in Huang Yin-Yaochang (Table 3). The results also showed that there is a resistance at different levels arising in the insect populations according to the dosage used in different places, (Table 4).