Abstract: To understand and grasp the current status of fish resources in the upper reaches of the Dadu River, this study conducted fish catch surveys and analyses at 42 sampling sites in the main stream and its tributaries from 2020 to 2023.The results showed that a total of 36 fish species, belonging to 3 orders, 8 families, and 22 genera, were collected in the survey area, including 24 indigenous species and 12 alien species.The indigenous fish were primarily composed of three major groups: Schizothoracinae (a subfamily of Cyprinidae), Nemacheilidae, and Sisoridae, totaling 21 species, which accounted for 75.00% of the indigenous species and 52.50% of the total species.The alien species were mainly from the family Cyprinidae, accounting for 50% of the alien species.The fish community structure in the upper Dadu River is undergoing changes, with the number and abundance of alien species continuously increasing, particularly in developed river sections.Due to habitat degradation and other factors, indigenous fish resources are declining.Some species that prefer rapids habitats are threatened or even disappearing, the trend of miniaturization is intensifying, and the number of alien species is multiplying.It is recommended to strengthen habitat protection and restoration, improve the ecological operation of existing hydropower stations, reduce water pollution, strictly combat illegal fishing, and implement control measures for alien fish species.