Abstract: In order to examine the composition, structure and diversity of fish assemblages in Xiliang Lake after fishing ban and identify key environmental factors affecting fish diversity, the investigation of fish assemblages and environmental factors was conducted in Xiliang Lake in November 2020 and April 2021, with 15 sample sites distributed in West-Xiliang Lake (XLH1-8) and East-Xiliang Lake (XLH9-15). The results showed that autumn was positively correlated with total nitrogen, chlorophyll a and chemical oxygen demand index, and West-Xiliang Lake was positively correlated with total phosphorus and turbidity. The results showed that a total of 31 fish species were collected belonging to 6 orders, 8 families, and 26 generas, among which the Cypriniformes (24 species) accounted for 77.4%. Toxabramis swinhonis, Hemiculter leucisculus, Carassius auratus, and Cultrichthys erythropterus were the dominant species, and Toxabramis swinhonis was the most dominant species. The results of Nonmetric Multidimensional Scaling indicated the significant seasonal and spatial differences in fish community structure in Xiliang Lake (P<0.05). Shannon-Wiener index, Simpson index and Pielou index of East-Xiliang Lake were significantly higher than that in West-Xiliang Lake in autumn (P<0.05), and Margalef index was significantly higher than that in West-Xiliang Lake (P<0.05); Functional richness index of East-Xiliang Lake was significantly higher than that in West-Xiliang Lake in autumn (P<0.05), and functional dispersion index was significantly higher than that in West-Xiliang Lake (P<0.05). Pearson correlation analysis exhibited that Shannon-Wiener index, Simpson index, Pielou index and Margalef index were significantly and positively correlated with functional richness index (r=0.66, r=0.61, r=0.50 and r=0.83) and functional dispersion index (r=0.93, r=0.89, r=0.89 and r=0.70; P<0.05). This result indicated that higher taxonomical diversity may contribute more functional space in fish assemblages. The results of the Redundancy Analysis indicated that total phosphorus were the key environmental factors driving fish species and functional diversity. This study provides a scientific basis for the recovery of fish resources and ecosystem restoration of lakes in the Yangtze River basin after the fishing ban, and provides a reference for future lake ecological protection policies.