In this study, photosynthesis and transpiration rates of Leymus chinensis were studied under controlled groundwater depths, using lysimeters. The lysimeter was 120 cm in length, 120 cm in width, and 300 cm in height. A shallow-water lysimeter was used to maintain water table depths of 1.0, 1.4, 1.8, 2.2, and 2.5 m in five independent soil columns. The experiment was conducted at the Da'an Sodic Land Ecological Experiment Station of the Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences. The soil type at the study site is classified as salt meadow soil. The experiment was conducted from June to September, in 2011 and 2012. The results indicate that variations in the net leaf photosynthesis and transpiration rates of Leymus chinensis showed a seasonal trend with a peak occurring in July or August. The diurnal change in the net photosynthetic and transpiration rates of Leymus chinensis was a typical bimodal curve with a depression that was observed at midday. Results also showed that groundwater depth has a strong impact on plant eco-physiological characteristics. When the groundwater depth ranged from 1.0 to 2.5 m, the net photosynthesis and transpiration rates of Leymus chinensis are highest when groundwater depth is 1.0 m, with a mean value of 22.6 μmol m^-2 s^-2 and 7.2 mmol H₂O m^-2 s^-1, respectively. Both net photosynthesis and transpiration rates of Leymus chinensis decreased as the groundwater depth increased. Leaf photosynthesis and transpiration rates of Leymus chinensis were correlated with groundwater depth during the growing season months: June, July, August, and September. Logarithmic or exponential correlations existed between the leaf photosynthesis and transpiration rates of Leymus chinensis and groundwater buried depth, at the following times: 6:00 a.m., 8:00 a.m., 10:00 a.m., 12:00 a.m., 14:00 p.m., 16:00 p.m., and 18:00 p.m. Determination coefficients (R²) for these correlation functions were > 0.9. These exponential or logarithmic correlations can be used to estimate the leaf photosynthesis and transpiration rates of Leymus chinensis in this area, when groundwater depth ranges from 1.0 m to 2.5 m. The results of this study provide useful information for the restoration of vegetation and the environmental protection of the Songnen Plain in China.