The coastal wetland in the Yellow River Delta has a shallow underground water level and is affected by both fresh and salt water. As a result, the conditions of the soil water and the presence of salt become the main factors affecting the key processes of the ecosystem. In addition, owing to global warming the average near-surface air temperature of the Yellow River Delta has risen significantly in the last 50 years (1961-2010). Warming can affect plant photosynthesis and photosynthetic characteristics both directly and indirectly, which affects the evolution of the coastal wetlands in the Yellow River Delta. A manipulative warming experiment was conducted in a coastal wetland of the Yellow River Delta using infrared heaters. The light response curve of Phragmites australis was measured during the growing season. During each light response curve measurement, soil environmental parameters were measured simultaneously, including soil temperature, moisture, and salinity. Based on soil moisture conditions, the entire growing season could be divided into three periods, the drought period, flooding period, and wet period. The results obtained were (1) During the drought period, soil temperature was significantly increased by warming by approximately 3.3℃, soil moisture increased by 9.4%, and soil salt content increased by 16.7% compared to the control. Similarly, photosynthesis of P. australis was suspended under intensive irradiation due to increased salt concentration. Meanwhile, warming significantly decreased the maximum net photosynthetic rate (Pnmax), dark respiration rate (Rd), light compensation point (LCP), and light saturation point (LSP). (2) During the flooding period, no significant differences in soil temperature, moisture, and salt content under warming were discovered. However, photosynthesis of P. australis was suspended due to the saturated soil water content. (3) During the wet period, warming increased the soil temperature at 10 cm depth by 3.0℃ and increased the soil moisture by 2.9%; however, had no effect on soil salt content compared to the control. Meanwhile, warming increased the photosynthetic rate under middle and high light conditions and increased Pnmax, Rd, and LSP significantly by 27.7%, 14.9%, and 23.3%, respectively. (4) During the entire growing season, soil temperature at 10 cm depth was significantly increased by warming by 2.9℃ and soil salt content was increased by 7.0% compared to the control. However, no significant effect on light responsive parameters occurred under warming conditions. Therefore, the effect of warming on photosynthesis is obviously controlled by the conditions of the soil water and concentration of salt in the wetland ecosystem.