To explore the effects of elevated CO₂ on photosynthesis characteristics and biomass allocation in Lycium barbarum. With L. barbarum seedlings as research materials， we applied open top chamber (OTC)， a facility to control changed CO₂ concentration to simulate natural environment in experiment. We conducted three gradients of CO₂ concentration， the control group is (380±20)μmol/mol（CK），which is ambient CO₂， and elevated was (570±20)μmol/mol（TR1）， （760±20）μmol/mol（TR2）. The effects of elevated CO₂ on photosynthesis and biomass allocation of L. barbarum seedlings were assessed by net photosynthetic rate（P_n）， light response curves， CO₂ response curves and dry weight during seedlings exposed to all three treatments （CK， TR1， TR2） after 90 and 120 days in 2017 and 2018. Results showed: （1） when treated for 90 days in 2017， the TR1 and TR2 in P_n of L. barbarum seedlings were increased significantly than that of control (P<0.05). After 120 days， the P_n of TR1 was decreased significantly compared with CK (P< 0.05). While P_n of TR1 was 4.77% lower than CK when we repeated the test after 90 days in 2018 (P>0.05). The treatment of TR1 and TR2 was higher in P_n than CK after 120 days，but the difference between them was not significant （P>0.05）. （2） With the rising of CO₂ concentration， it is similar that the intercellular CO₂ concentrations (C_i) of TR1 and TR2 treatment were soared respectively than ambient CO₂ in 2017 and 2018 (P<0.05). With the time prolonging until 120 days， the stomatal conductance (G_s) of TR1 and TR2 dropped conspicuously than that of CK (P<0.05). No difference in water use efficiency （WUE） in 2017， but it raised obviously than control after 120 days in 2018. （3） At 90 days， the light saturation point and CO₂ saturation point of treatment TR1 and TR2 were all rising than control， which was maintained in 120 days，but the CO₂ assimilation rate of TR2 was declined. （4） The biomass allocation of L. barbarum seedlings increased signally in its aboveground with CO₂ rising， thus less allocated in underground organs （P<0.05）. We concluded that slightly elevated CO₂ could promote the photosynthesis of L. barbarum seedlings， as a result of photosynthesis， the biomass accumulation in L. barbarum seedlings was tend to its aboveground organs， while underground was reduced remarkably. With the concentration and incubation time extending， the photosynthesis in L. barbarum seedlings showed a downregulation trend， which revealed by its P_n， G_s and photosynthetic CO₂ assimilation rate decreased.