Mastering the distribution of species composition and their abundance of fishes is basic for the conservation and management of fish diversity. Based on the data collected from Chuhe River in December 2015 and May 2016, we examined how the fish assemblages vary spatially and seasonally in this study area. A total of 4 798 individuals representing 45 species were collected, a total of 45 fish species belonging to 37 genera, 13 families, and 6 orders were collected during the investigation, with cyprinids accounting for 55.56% of the collected species. One-way ANOVA indicated that there were no significant seasonal differences in fish diversity,however, notable differences in fish diversity were observed among sampling sites. Carassius auratus, Cyprinus carpio, Abbottina rivularis, Pseudobagrus fulvidraco, and Pseudobrama simoni, were the dominant species. Omnivorous and detritivore fish species were the most frequent of the four feeding functional groups, which account for 63.04% of the total, and sedentary fish species (89.13%) were the most frequent of the three ecological groups, whereas demersal fishes (45.65%) were the most frequent of the three habitat types. Large commercial fishes account for a very small percentage of the whole fishes and the relative importance index (IRI) value is low. Analysis of species richness and diversity indicated that the fish diversity of the downstream of Chuhe River was low, with great spatial variation. The species richness and diversity of the upstream of Chuhe River was high, while the fish species in Qinliu River and Lai'an River take the second place. Fish species were similar between two seasons, and fish assemblage structures showed no significant difference between seasons. Variations among different reaches were observed for both fish species diversity and assemblage structures. Generally, the downstream of the river had relatively lower species diversity, while those in the upstream were relatively higher. Obviously fish community overlaps, hardly any separation were observed between seasons, when the spatial variations in fish assemblages among sections were considered, fish assemblage structures, not species diversity, showed significantly variation. Fish assemblage structures variation were mainly due to the spatial distribution of some dominant fishes, such as Carassius auratus, Cyprinus carpio, Abbottina rivularis and Pseudobagrus fulvidraco.