In view of the potential ecological problems of the reduction in the area and quality of fish habitats due to changes in the flow processes in the lower reaches of the hydraulic engineering after its completion and operation, the habitat simulation method was used to study the environmental flow in the 4. 9 km section of the proposed Xi County hub project. By using the method of combining MIKE numerical simulation with HSI habitat model, this paper discussed the effects of different flow rates on fish habitat in different life stages and determine the appropriate flow range by analysis of the water flow characteristics and the status of fish habitats in the study river section under natural conditions, providing theoretical and methodological guidance for the protection of aquatic habitats after hydraulic engineering construction.