Eucryptorrhynchus chinensis (Olivier) is one of the most important pests of Ailanthus trees. The orphology, living habits, life cycle and behavior of the pest is described. There is one generation per year. Both adults and larvae hibernate in soil and generations overlap. The eggs last 7～10 days. The larva has six instars. The execrate pupa appears from the end of April to May, the end of July to early August and adults emerge after 10～14 days. The adult weevils feed on tissues of bud and phloem by the long beak .The young larvae feed on tissues of liber and the elder larvae bored in layer of wood. The adults had thanatosis and phototaxis habit and the peak of daily activity was 11:00～17:00. Female and male adults can mate repeatedly and each copulation lasted 10 to 20 min. About 20 to 40 mins later, they can mate again. After the copulation, the female could feed with the male mounted on back for 20 to 30 mins. The females gnawed a hole in the bark and laid an egg in about 15 min. On average, one female laid about 40 eggs in the reproductive period.