Abstract: The lower reaches of the Jinsha River is a national nature reserve for rare and endemic fishes, and an appropriate ecological flow is one of the necessary conditions for fish spawning and reproduction. In order to quantify the appropriate ecological flow required for spawning and reproduction of the four major Chinese carps, the Xiangjiaba Dam to the Yibin hydrologic station in the lower reaches of the Jinsha River was taken as a study area, the hydrodynamic requirements (velocity and water depth) of the habitat during the spawning period of the four major Chinese carps were taken as the main ecological factors, and the hydrodynamic suitability curve of the four major Chinese carps was established based on the measured data from 2012 to 2019. We also established a depth-averaged two dimensional hydrodynamic model based on unstructured irregular triangular grid to realize the hydrodynamic distribution characteristics of the fish habitat. The physical habitat simulation model (PHABSIM) was used to analyze the main hydrodynamic conditions (velocity and water depth) that affect the spawning of the four major Chinese carps, and quantify the weighted usable area (WUA) of the four major Chinese carps under different release from the Xiangjiaba Reservoir. Using the relationship curve between release and the WUA of habitat was obtained, the influence of different release from the reservoir on the WUA was discussed, and the appropriate ecological flow was selected accordingly. The results showed that the appropriate velocity during the spawning and reproduction period of the four major Chinese carps was 0.6-1.3 m/s, the most appropriate flow velocity was 0.9-1.0 m/s, and the appropriate water depth was 3.0-18.0 m, the most appropriate water depth was 9.0-12.0 m. The WUA of the habitats increased first and then slowly decreased with the increasing of discharge. When the release from the reservoir is 3000 m³/s, the WUA was the largest, accounting for 24.26% of the study area. So the appropriate ecological flow range was 2000-4500 m³/s, and the most appropriate ecological flow was 3000 m³/s. The research shows that by controlling the appropriate outflows of the Xiangjiaba Reservoir, the habitat area of the four major Chinese carps in the Yibin River section can be effectively guaranteed, which provides a scientific basis for improving the hydrodynamic conditions of the spawning sites through ecological regulation of the cascade reservoirs in the lower reaches of the Jinsha River.