Human-mediated introduction of cosmopolitan species and extirpation of endemic species modify community similarity, resulting in community-distinctiveness decrease or increase. Data from four basins in the Wannan Mountains, China, was used to evaluate the effects of low-head dams on patterns of fish faunal homogenization and differentiation based on abundance data. We aimed to examine the spatial changes in taxonomic and functional similarity of fish assemblages driven by low-head dams, and whether the changes in fish assemblage similarity differed between taxonomic and functional components. We found that low-head dams significantly decreased the mean taxonomic similarity but increased the mean functional similarity of fish assemblages in impoundments for abundance-based approaches, suggesting that taxonomic differentiation accompanied functional homogenization in stream fish assemblages. Meanwhile, these results showed the importance of population abundance in structuring fish faunal homogenization and differentiation at small scales, especially when the major differences among assemblages are in species abundance ranks rather than species identities. Additionally, we also found only a weakly positive correlation between changes in mean taxonomic and functional similarity, and partial pairs exhibited considerable variation in patterns of fish faunal homogenization and differentiation for taxonomic and functional components. In conclusion, our study proved that changes in taxonomic similarity cannot be used to predict changes in functional similarity. Keywords: Low-head dam, Stream fish, Biotic homogenization and differentiation, Taxonomic and functional diversities