Abstract:The research has been done by using HPLC in order to measure the content of six kinds phenolic acids in seven strains of poplars’ phloem, and observe the resistance to the Xylotrechus rusticus Linnaeus by applying to exogenous phenolic acids. There is significant different level of content of each phenolic acid in different strains of poplar. The content of the six phenolic acids measured had positive correlation with each other, some of which reached a significant level. The six exogenous phenolic acids have effect on the resistance of Xylotrechus rusticus to different extents, especially in caffeic acid, cinnamic acid and syringic acid, the rate of resistance in which is more than 78%.