Gras exchange parameters of three new poplar clones (JK-7，JK-10，and JK-11) and the correspond ing environmental factors were measured in order to explore the relationships of net photosynthetic rate (Pn),Transpiration rate(Tr),water use efficiency(WUE)，and the environmental factors such as photosyn-thetically active radiation (PAR)，air temperature(Ta)，vapor pressure deficit (VPD)，and relative humidity (RH}.Results showed that the three clones were different in response to the same environmental factors.The diurnal courses of P and T,displayed single peak curves in JK-7 and JK-11 and a double peak curve,in JK-10,while the diurnal courses of WUE displayed double-peak curves in all clones. There were significant differences in P and T,among these clones(P<0.05),with the highest in JK-10 and lowest in JK-7,and they were significantly higher in JK-10 than in JK-7.There was no significant difference in WUE among these clones. The Pn and Tr,had close correlations with stomatal conductance(Gk)and PAR in the three clone s,while they had close correlations with RH in JK-7 and Tuain JK-10. There was significant negative correlation between WUE and Gk in the clones.