Abstract: In this experiment, 3-4monthold Populus tremuloides seedlings were used as materials for controlled water test by soil progressive drought method, and then the leaf relative water content (RWC), stem xylem water potential (ψxp), fluorescence parameters, gas exchange and leaf area index were measured to comprehensive evaluation of drought resistance of poplar seedlings. The results showed that leaf RWC, ψxp, stomatal conductance (gs) and net photosynthetic rate (Pn) were decreased significantly at the early stage of drought. To stage 2, these parameters almost dropped to their valleys, and they had no obvious variation even implemented continue drought. After all leaves were dead and remained one month no watering, and then rewatered, new leaves grow from the old leaf position. Leaf RWC and ψxp of new leaves returned to the control level, but Pn and gs had no obvious increase. Under severe drought stress damage, Pn and gs reduced significantly, and photosynthetic system repair was relatively slow, and even some was irreversible damage. The photochemical quantum yield (Fv/Fm) was more stable, and less affected by drought stress.