Abstract: As a typical environmental stress factor,UV-B radiation could make a significant impact on the growth,development,and physiological metabolism of plants,and it could be of great significance to understand the defensive response of wood species poplar to UV-B radiation. In this study,84 K poplar seedlings used as materials were subjected to different intensities of UV-B radiation. The contents of six defensive phenolic acids in 84 K poplar seedlings before and after the stress were analyzed,and the accumulation mechanism of target compounds was discussed from the perspective of photosynthetic pigments and ROS system.The results indicated that the proper UV-B treatment was helpful for the accumulation of five target phenolic acids（ferulic acid,caffeic acid,protocatechuic acid,chlorogenic acid and isoferulic acid）,especially the content of chlorogenic acid increased about 15 times after 8 h of UV-B radiation;the accumulation trend of photosynthetic pigments was the same as phenolic acids,and the content of total chlorophyll increased 1.21 times after 16 h of UV-B radiation;antioxidant enzymes（especially POD）were found cooperate with phenolic acids to resist the oxidative stress caused by UV-B radiation. Overall,this study provided a theoretical basis for elucidating the metabolic regulation mechanism of defensive phenolic acids in poplars under UV-B radiation stress.