Vegetation plays an important role in preventing wind erosion, sand fixation, water conservation and ecosystem restoration in oasis ecosystem. For the photosynthetic characteristics could fairly reflect the adaptation of plants to their habitat, gas exchange parameters and environmental factors of three different life-form plants which grown in the desert-oasis ecotone of Keriya River Basin were measured. By comparing the photosynthetic characteristics of Phragmites australis, Tamarix ramosissima, Populus euphratica and their relationship with environmental factors, adaptive capacities and mechanisms of the three different life-form plants were discussed. The results were as follow: The diurnal variation in net photosynthetic (P_n) rate of the three plants showed two peaks, which displayed remarked photosynthetic "midday depression". The order of the average values of P_n was: P. euphratica > P. australis > T. ramosissima. However, there was no significant difference among them. The analysis of partial correlation and path on P_n and environmental factors showed that the diurnal variation of P_n had significant correlation with transpiration rate (T_r), photosynthetically active radiation (PAR), and stomatal conductance (G_s), respectively. T_r, PAR and G_s were the main factors which affected P_n of P. australis and the order of effecting ability was T_r > G_s > PAR. T_r, and G_s were the main factors which affected P_n of T. ramosissima and the order of effecting ability was T_r> G_s. T_r was the only main factor which affected P_n of P. euphratica. For the three kinds of plants, the P_n-PAR response curves and P_n-CO₂ response curves had the same changing tendency, which could be quantitatively described by quadratic equation, respectively. The order of light compensation points and light saturation points were both T. ramosissima > P. euphratica > P. australis. The order of carbon dioxide compensation points was P. euphratica > T. ramosissima > P. australis and the order of saturation points were P. euphratica > P. australis> T. ramosissima. The apparent quantum yield and carboxylation efficiency of these three plants were varied from 0.0341 to 0.0411 mol/mol and 0.0480 to 0.0546 mol m^-2 s^-1 on daily basis, respectively. The results indicated that the average net photosynthetic rate, energy efficiency and CO₂ assimilation capacity were not significantly different among the three kinds of plants, and the photosynthetic "midday depressions" was mainly resulted from stomatal limitation. The main factors which affected physiological process of photosynthesis are different among the three different life-form plants, but the relationship between T_r and P_n is closer than other factors.