Abstract: In order to understand the current status of fish assemblages in the Three Gorges Reservoir, both species composition of fish in the mainstream and nine important tributaries of the Three Gorges Reservoir, and fishery resources in the upper (Mudong section), middle (Yunyang section) and lower (Wushan section) reservoir were investigated, from 2017 to 2019. The changes of fish assemblages before and after impoundment were also analyzed by comparing the present results with other published data. A total of 149 fish species, belonging to 10 orders, 25 families and 92 genera, were collected in the Three Gorges Reservoir, of which 30 species were endemic to the upper reaches of the Yangtze River, 20 species were exotic, 67 species were rheophilic and 82 species were non-rheophilic. Compared with historical records of fish species before the impoundment of the Three Gorges Reservoir, the total number was similar. However, the species composition of fish has undergone a remarkable change after the impoundment. The number of both native and rheophilic species dropped notably, whereas that of exotic species increased remarkably. Small-sized fishes accounted for a great proportion in fish catches, while the catches of the middle and large sized fishes declined severely. Rheophilic species only dominated in the catches of the upper reservoir, while non-rheophilic species were dominant in the middle and lower reservoir. Both the number and resources of the endemic species were reduced significantly in the mainstream of the Three Gorges Reservoir, whereas a certain number of endemic species still exist in the tributaries. Exotic species constituted a considerable proportion of fish catches in the middle and lower sections of the reservoir, which suggests that the high abundance and dispersion of these alien species may bring noticeably negative influence to the survival of native species. In conclusion, fish assemblage of the Three Gorges Reservoir has been changed to a great extent by the impoundment.