Identifying critical hydrologic parameters that structuring biological communities is crucial for the conservation and restoration of wetland ecosystems. The present study determined the key parameters of water level fluctuations (WLFs) influencing the distribution of a typical wetland plant, Carex, in shallow lakes along the middle and lower reaches of the Yangtze River. The plant community and environmental variables in 13 shallow lakes with different WLFs were investigated during 2011-2015. A total of 14 parameters included in three components of WLFs were identified, and their effects on the distribution of Carex were analyzed. The results showed that distribution of Carex in the studied lakes differed obviously in time and space. WLFs were the critical factors influencing the taxa distribution, whereas soil organic matter, human disturbance, substrate type, and soil moisture were of little importance. Rate of water level change and elevation above water were the main parameters determining the coverage and biomass of Carex during the spring growing season. In the autumn growing season, rate of water level change, elevation above water, and emergence timing were important. These results provide important insights into the conservation and restoration of Carex and other hygrophytes in shallow lakes in this region.