Abstract: Coscinesthes salicis, a longhorn beetle which bore the trunk and branch of poplar and willow in larvae phase, may destroy the branches or even lead the trees to death.More than 90 percent of the life cycle of this pest insect is spent inside the tree.Through the artificial feeding in the laboratory and the field investigation in past three years, the observations on the biological characteristics of larvae and pupae, the color changes as well as the development progress within the period from larva to pupae were made.Besides, the minimum temperature for development and the accumulative temperature were also tested.With eleven instars, Coscinesthes salicis have one generation every two years, and spend the winter in form of full-blown larva and egg in Kunming district.These results provide reliable scientific basis for developing effective management strategy.