Abstract: The net photosynthesis(Pn),the daily courses of Pn,transpiration rate(TR),stomatal conductance(COND),water use efficiency(WUE) and dark respiration(DR) of Quercus variabilis under ambient and elevated CO₂ conditions were determined with Licor-6400 photosynthesis system.The results are as follows(1) Compared to the ambient air CO₂ concentration(400 μmol CO₂·mol^-1),Pn and quantum efficiency under 800 μmol CO₂·mol^-1 were significantly increased.Furthermore,the light compensation point decreased while light saturation point elevated.(2) The daily courses of Pn under ambient CO₂ concentration were double peaked,however under 800 μmol CO²·mol^-1 they were single peaked.(3) Under elevated CO²(800 μmol CO₂·mol^-1),COND,TR and DR reduced,and WUE increased significantly.It was concluded that the increasing CO₂ concentration in the atmosphere would be beneficial to Quercus variabilis and the Quercus variabilis forest would slow down the pace of CO₂ increase.