Abstract: Dongting Lake, as the second largest natural lake connected to the Yangtze River in the middle and lower reaches, is an important habitat for the four major Chinese carps in the Yangtze River and possesses irreplaceable ecological functions and economic value. Based on the hydrological and topographic data of Dongting Lake from 2016 to 2020, this study constructed a two-dimensional hydrodynamic model of Dongting Lake, simulated the flow velocity and water depth distribution of Dongting Lake from 2016 to 2020, and established the flow velocity and water depth suitability curves for the fattening of juvenile and adult fish of the four major Chinese carps in combination with literature data. The changes of Habitat Suitability Index (HSI) and Weighted Usable Area (WUA) from July to October 2016-2020 were calculated, and the relationship between WUA and the water level of Chenglingji in Dongting Lake was fitted. The suitable ecological water level of Dongting Lake has been determined. The results show that: (1) The optimal flow rate for fattening juvenile fish of the four major Chinese carps in Dongting Lake by rope feed is 0.1-0.2 m/s, and the optimal water depth is 0.7-1.6 m. The optimal flow rate for fattening adult fish by rope feed is 0.1-0.3 m/s, and the optimal water depth is 2.0-4.0 m. (2) From 2016 to 2020, the average monthly flow velocity and water depth of Dongting Lake from July to October basically showed a gradually decreasing trend. The flow velocity of South Dongting Lake was relatively high, while that of East Dongting Lake was relatively high. In 2020, the overall average monthly flow velocity and water depth were relatively high compared with other years. (3) From 2016 to 2020, the average monthly HSI and WUA ranges of juvenile fish of the four major Chinese carps in Dongting Lake during July and August were 0.004-0.14 and 12-402 km2 respectively, and those of adult fish during September and October were 0.05-0.23 and 146-683 km2 respectively. Juvenile and adult fish have the highest suitability in the non-mainstream area of South Dongting Lake. (4) The suitable ecological water level for fattening juvenile fish of the four major Chinese carps in Dongting Lake by using bait is 26.9-28.0 m, corresponding to a WUA of 342 km2, accounting for 13% of the total area. The suitable ecological water level for fattening adult fish by using bait is 29.0-30.0 m, corresponding to a WUA of 832 km2, accounting for 32% of the total area. The research results provide a reference for the protection of the Dongting Lake ecosystem. Key words: Dongting Lake; The four major Chinese carps; Feeding and Fattening of Juvenile fish; Feeding and Fattening of adult fish; Ecological water level