Abstract: Coastal wetlands are widely recognized as efficient carbon sink. However, the effects of ecosystem salt redistribution due to sea level rise or human activity on plant photosynthesis have not been fully studied. In this study, Phragmite australis growing in natural salinity gradient of 1.1, 7.1, 16.1 psu in the Yellow River Delta were selected as the research objects. The photosynthetic parameters, light response curves, and CO₂ concentration response curves across different seasons were measured using a portable photosynthetic fluorescence measurement system (Li-6800, LI-COR, USA). The growth characteristics and chlorophyll content were measured simultaneously. Results reveal that salinity reduced the shoot height and basal diameter of P. australis, and high salinity retarded the growth of shoot height. In July, when the average ambient temperature exceeded the optimum temperature of 25 ℃ for photosynthesis of P. australis, the photosynthetic rates (P_n) in 7.1 and 16.1 psu salinity environments were significantly lower than that in the 1.1 psu salinity environment. However, in September when the average temperature was relatively lower, P_n of P. australis in 16.1 psu was higher than that in lower salinity environments. In particular, the maximum net photosynthetic rate (P_nmax and A_nmax) of P. australis in medium-salinity environments could be up to 40.3% higher than that in low- and high-salinity environments. These findings suggest that future sea level rise may enhance the carbon sequestration potential of P. australis wetland distributed in the freshwater environments of the upper delta plain. Additionally, this study has significant implications for related disciplines to improve salt-tolerant crop varieties and restore ecosystems in saline-alkali lands.