Abstract: This paper explores the adaptive mechanisms of three forage grasses (Bromus inermis, Dactylis glomerata and Poa pratensis) that are predominant in Sinkiang natural grasslands. Using pot experiment methods, drought stress was simulated to determine the effects of three different soil water contents levels (80%, 60% and 30% of field water capacity) on leaf photo-physiological characteristics and water use efficiency (WUE). With decreasing soil water contents, the daily average value of intercellular CO₂ (C_i) in the three grasses increased. The daily average values of stomatal conductance (G_s), net photosynthetic rate (P_n), transpiration rate (T_r), the ratio of P_n to C_i and evapotranspiration decreased, but the variation ranges of these characteristics differed across the three grasses. As drought stress increased, the daily average accumulated biomass of P. pratensis significantly decreased (P<0.05), but there was no obvious change in the other two grasses (P>0.05). The net water use efficiency (WUE_ET) and the daily average value of instantaneous water use efficiency (WUE_i) of D. glomerata changed very little (P>0.05), but in the other two grasses both WUE_ET and WUE_i significantly decreased (P<0.05). The WUE_ET of P. pratensis was significantly positively correlated with its daily average values for T_r and evapotranspiration (P<0.05). The WUE_ET of the three forage grasses was significantly positively correlated with their daily average accumulated biomass (P<0.05). The WUE_i and WUE_ET of the three grasses followed different change trends with the decrease in soil water contents. This study suggests that the adaptability of the three forage grasses to arid environments depends not only on their WUE but is also related to their biological characteristics and life history strategies.