Abstract: This paper deals with the complication of number of generations and generation differentiation of pine caterpillars, which include Dendrolimus superans (Butler), D.spectabilis Butler, D.punctatus and D.tabulaeformis Tsai et Liu etc.in USSR, Japan and China.The number of generations of pine caterpillars varies in different areas.In general, there is one generation in 1-3 years for D.superanus, passing 2-4 winters, 1-3 generations a year for D.tabulaeformis and D.spectabilis, 2-5 generations a year for D.punctatus.Generation differentiation is a common occurrence, which is caused by larval diapause.Differentiational rate varies greatly in the population of Dendrolimus spp.in different plots, even in the same plot, it varies in different years too.The diapause of pine caterpillar is relevant to the larval hatching period, food, climate and other ecological conditions.In the paper, some ideas about "a study of developmental threshold and effective accumulated temperature of D.tabulaeformis" in the "Scientia Silvae Sinicae" 1987, 23(3), have also been put forward.