In freshwater lake wetland ecosystems, hydrological conditions are the key factors affecting the distribution of vegetation and plant growth. It is of great importance to elucidate the relationships between plants and hydrological conditions to understand the formation of wetland vegetation patterns and provide appropriate references for ecological regulation and wetland ecosystem restoration. This study was conducted using field surveys on the height, density, and biomass of a Carex cinerascens population along an elevation gradient in Poyang Lake wetland to assess the variation in productivity of the C. cinerascens population during the spring growth season and its response to hydrological conditions. The results showed that the ecological indicators of the C. cinerascens population presented the same trends in different elevation zones during the spring growth season, whereas the spatial heterogeneity of hydrological conditions had an obvious effect on the growth of the C. cinerascens population. It was confirmed that long-term continuous flooded and semi-flooded conditions severely inhibited the growth of the C. cinerascens population and caused C. cinerascens to undergo quiescence syndrome of dormancy or slow growth. The intermittent semi-flooded and non-flooded conditions can promote the growth and biomass accumulation of C. cinerascens, which usually adjusted its water use strategy in different growth stages according to the field hydrological conditions. In the early growth stage, C. cinerascens responded to drought stress by increasing the water content of the plant, whereas it accumulated dry matter in the late growth stage during flooding stress. In addition, hydrological conditions greatly affected the colonization and growth of C. cinerascens. During the two adjacent spring growth seasons, C. cinerascens could benefit from hydrological conditions with average inundation water depth of 2.78-3.93 m, inundation frequency of 42.10%-60.38%, and the water height from the water surface of -1.73-0.77 m. Hydrological conditions with an average inundation water depth of 3.70-2.78 m, inundation frequency of 42.08%-43.17%, and average height from the water surface of -0.23-0.77 m were more conducive to the growth of C. cinerascens. These results could provide an important reference for wetland vegetation protection and water level regulation in the Poyang Lake wetland.