Abstract: The net photosynthetic rate (P_n), transpiration rate (T_r), water use efficiency (WUE), stomatal conductance (G_s), intercellular CO₂ concentration (C_i) and vapor pressure deficit (V_pdl) of four Elymus species were determined under simulated photosynthetic radiation (SPR) and the apparent quantum yield (AQY), light saturation point (LSP) and light compensation point (LCP) were calculated. The P_n and T_r increased with an increase in SPR in all four species. Under the same light intensity, E. tangutorum had the highest P_n of the four species, while E. dahuricus was medium, and the other two species had almost the same P_n. The T_r of E. tangutorum and E. excelsus were significantly higher than those of E. sibiricus and E. dahuricus. The WUE also increased with an increase in SPR, and the order of WUE for the species was E. sibiricus＞E. dahuricus＞E. tangutorum＞E. excelsus. The G_s increased with an increased SPR. The G_s of E. tangutorum and E. dahuricus were significantly higher than those of the other two species. The C_i decreased with increases in SPR and P_n. The V_pdl first dropped with an SPR increase from 0 to 500 μmol/(m² · s), and except for E. dahuricus, the other two species then showed an increase in the V_pdl with an SPR increase. Overall, the V_pdl of E. tangutorum and E. excelsus were significantly higher than those of the other two species. In addition, E. sibiricus and E. tangutorum had lower LCPs than the other species, indicating their higher ability to use light under low-light conditions. Both E. tangutorum and E. dahuricus had a high LSP among, showing their better ability to use strong light. In conclusion, E. tangutorum and E. dahuricus had a relatively higher capacity for light utilization than E. sibiricus and E. excelsus; that is, they had higher photosynthetic efficiency whether under high or low-light conditions.