Abstract: In order to investigate the effects of spur dikes in Beijiang River on fish habitat, we took the Yingde section in the main stream of the Beijiang River as a study area, chose the typical dominant fish,Carassius auratus,as the target species, and used the unstructured-grid finite-volume method computational model(FVCOM) to calculate the weighted useable area(WUA) ofCarassius auratushabitat under different flow conditions, and determined the optimal ecological flow value for the fish.Based on the derived fish optimum ecological flow values, the effects of spur dikes on flow velocity, water depth, fish habitat suitability index and hydraulic habitat diversity were studied.The results show that when the upstream flow is at the optimum ecological flow rate of 350 m3/s, the spur dikes cluster makes the WUA value decrease from 7.142 km2to 5.692 km2.Spur dikes significantly alter flow velocities in the center of the channel and nearshore, resulting in a decrease in the flow suitability index, which in turn decreases the habitat suitability index for the entire study area.The backwater effect of spur dikes is limited, with a maximum backwater depth of 0.38 m, which has a small effect on the distribution of the bathymetry suitability index.The percentage of area with high habitat acceptability decreases from 52.151% to 32.271% under the action of spur dikes, reducing fish habitat quality.Spur dikes reduce the Simpson′s Index of Hydraulic Habitat Diversity from 0.547 to 0.529,resulting in a slight decrease in hydraulic habitat diversity within the study area.The results of this research can provide a reference basis for protection and ecological restoration of fish habitat in the Beijiang River.