In this study,we investigated that the effects of ultravioletB radiation and NaCl stress and their combined treatments on the antioxidant system and photosynthetic pigments in two species of poplar,Populus euphratica and Populus russkii (black poplar hybrids),by setting four treatment groups including UV-B(enhanced UV-B radiation),NaCl(100 mmol/L NaCl),UV-B+NaCl(enhanced UVB radiation and 100mmol/L NaCl),CK(No extra NaCl and UV-B treatment).The results show that:(1)under enhanced UVB radiation and NaCl stress and their combined stresses,the content of chlorophyll of two species of Populus were decreased,the ratio of chlorophyll a/b was also decreased,but the content of carotenoid was increased.The contents of lipid peroxidation MDA and H₂O₂ in leaves of P.euphratica and P.russkii were both significantly increased (P<0.05).However,under the combined stresses,the MDA content in leaves of P.russkii was significantly lower than each single stress,the MDA content in leaves of P.euphratica and the H₂O₂ content in leaves of P.euphratica and P.russkii were between two singlestress.(2)The activities of POD and CAT in P.russkii and P.euphratica were all significantly increased under three different stresses,and POD activity was the highest under the combined stress.(3)The contents of osmotic protectants (such as proline,gylcinebetaine,soluble protein)in leaves of two species of populus were all significantly increased under three different stress conditions.Moreover,the contents of proline and soluble protein were the highest under the combined stresses.Compared with P.russkii,the content of gylcinebetaine in leaves of P.euphratica had larger increase in under three different stresses,while the content of soluble protein of P.russkii was significantly more than P.euphratica under enhancement of UV-B radiation and the combined stresses.In summary,two species of Populus were subject to different degrees of damage under three different stress conditions.But compared with two kinds of single stress,the antioxidative ability of two species of Populus was the strongest under the combined stresses,so the degree of two species of Populus damaged was more less under the combined stresses.It show that the enhanced UV-B radiation and NaCl stress may antagonized each other’s effects in plantlet.