Abstract: The juniper bark borer Semanotus sinoauster Gressitt is one of the main borer pest of the Chinese fir.The insect has one generation a year in Zhengxiong County,Yunnan Province,a small part of its population can finish two generations in one year,which over winter by adults in pupal chambers.The adults come out of the tree trunk and mate up in middle March.Each adult lays 44 eggs in average.The larval stage lasts from middle March to late September.The pupal stage lasts from early August to early September.From middle August to late September,the adults emerge and stay in pupal chamber to overwinter.The adults lay eggs individually in bark cracks or under bark of the weak or dying trees,a small number of adults lay 2-4 eggs together.The life-table data of the insect shows that natural enemy preying,tree resin drowning,and germ infecting are the key factors to control its natural population.Investigating results also show that the occurrence of the insect is influenced by forest age,slope site,and forest management measure.The reproduction and development of the borer can be effectively limited by thinning,cutting and felling the infected trees.