Abstract: The poplar-trunk clearwing (Sphecia siningensis Hsu) is a new important insect pest of poplar trees in Qinghai province.It took 2 years to complete its life cycle which may extend over 3 years, in Sining, The adults show emergence period characterized by main group and non-staple group, which reach maxima in August and June respectivelly. The early boring stage of the larval occurred in mid and late July and late September to mid October mainly. The larval stage was seen to consist of 8 instars. The larvae can grow 1 to 4 (or 5) instars in the first year, and 6 to 8 instars in the seconed year. The larvae bore into the xylem alburnums in L-shaped burrows, and all will cocoon, pupate, emergence in its burrows in the third year. Therefore, a lot of the adults and the larvae of the pest population are always presented in each year, due to the succession between different year-group.The females lay the most eggs at the place within 1 m of D. B. H. and at the base of crown near the point of branches. 1. In the early boring stages to spray the tree trunks with 50% Phosphamidon in concentrations 1:50 to 1:100 was good to kill the new larvae. 2. To inject into the burrows on the trunks 40% Rogor or 80% Dichlorvos crude emulsion was effective to kill the older larvae.