Abstract: Influence of FA on photosynthesis and transpiration rate of Populus Euramericana was researched.The result showed the effect of FA of 3.5 g•L-1 is the Best,which reduced stomatal conductance and transpiration rate by 29.1% and 26.3% Respectively; FA could promote photosynthetic rate;The leaf water potential was improved by 14.3%,it had an obvious prohibiting effect on the decrease of leaf water potential.