To analyze the relationship between different outflows from Three Gorges Reservoir (TGR) during the drawdown period and the weighted usable area (WUA) of sedentary fish spawning habitat in Dongting Lake, the water depth and flow velocity were selected as the key influencing factors of sedentary fish spawning habitat, and the habitat suitable curves were established. This study quantitatively assessed the spatial variation characteristics of fish spawning habitat suitability based on the physical habitat simulation model (PHABSIM), and quantified the suitable ecological flow required for the fish spawning. The results show that the increase of outflow from TGR during the drawdown period has a certain effect on the water level and flow velocity of Dongting Lake. The effect on East Dongting Lake is obvious, but the effects on South Dongting Lake and West Dongting Lake are less. With the increase of outflow, the WUA of sedentary fishes spawning habitats in the lake area first increased and then decreased, whilst the difference is that the WUA of East Dongting Lake shows a gradual upward trend, the WUA of South Dongting Lake has a small overall increase with a double-peak curve, and the WUA of West Dongting Lake shows a trend of decreasing after increasing. The suitable ecological flow range of sedentary fishes spawning habitat was 18 500-24 500 m³/s, and the optimum ecological flow is 22 500 m³/s.