Study on the photosynthetic physiology characteristics and osmolytes of Alhagi sparsifolia under different irrigation grads was carried out. The results showed that the soil water content and leaf chlorophyll content of Alhagi sparsifolia all increased after irrigation. At the same time, the transpiration rate (Tr) and intercellular CO2 concentration (Ci) increased with the increasing of stomatal conductance (gs). These further accelerated the process of photosynthesis. The light compensating point and apparent quantum efficiency of Alhagi sparsifolia increased after irrigation, which expressed that irrigation had increased the light use efficiency and degree of Alhagi sparsifolia. Photosynthetic rate and respiration rate both increased with the increase of irrigation quantity, which indicated that the physiological metabolization of Alhagi sparsifolia was more active in better water condition, meaning higher material synthesizing and higher consumption. In addition, free proline could accumulate largely under drought stress, which showed that free proline plays an important role in drought resistance of plant. Irrigation in Summer can effectively improve the soil water condition and increase the productivity of photosynthesis.