Understanding the eco-physiological response characteristics of Phragmites australis to water-salt condition is the key of determining the threshold of wetland ecological water requirement, in order to supply a feasible method for calculating the wetland ecological water requirement and scientific base for wetland restoration. By field investigation of Phragmites australis in Momoge wetland, we analyzed the relationship between eco-physiological characteristics of Phragmites australis and water-salt gradient with method of redundancy analysis (RDA) by using CANOCO software in Version 4.5. The results showed that the combination of three environmental factors including water depth, Na⁺ and HCO₃^-, explained 54.7% of the variation of eco-physiological responses of Phragmites australis, suggesting that the three environmental factors led to great changes in eco-physiological responses of Phragmites australis. Water depth was the key environmental factor influencing the growth of Phragmites australis. There was a significant positive correlationship between water depth and the eco-physiological characteristics including plant height, biomass, chlorophyll content, maximum photosynthesis efficient (F_V/F_M) and maximum photosynthesis performance index (PI_ABS). There was no significant correlationship between Na⁺/HCO₃^- and the characteristics of Phragmites australis. The results suggested that it is the key point in the process of wetland restoration in mild or moderate saline-alkaline wetland to consider the influence of water depth on the growth of Phragmites australis, and secondly consider the effect of Na⁺/HCO₃^-, and determining the ecological water depth and fulfilling the ecological water requirement.