Shijiu Lake is the only river-connected lake in the lower reaches of the Yangtze river. To determine the status of its fish resources, this study used multi-mesh gill nets and customized series cage pot to collect fish in the Shijiu Lake in the season from January 2017 to March 2018, and analyzed the fish community structure and seasonal changes in the Shijiu Lake. Our subsequent results showed that a total of 36 species of fish were collected, belonging to 28 genus, 7 families and 6 orders, among which Cyprinidae was the most common, accounting for 69.4% of the total species. The fish species were primarily sedentary, omnivorous, and pelagic fish with 25 small fish accounting for 69.44% of the total species. Toxabramis swinhonis, Coilia nasus, and Carassius auratus were the dominant species of the Shijiu Lake throughout the year. In addition to the dominant species throughout the year, the seasonal unique dominant species are Pseudorasbora parva in spring, Culter alburnus and Hemiculter leucisculus in summer, Pseudobrama simoni in autumn and Hemiculter bleekeri in winter. The relative density and biomass of fish showed marked seasonal variation, but the variation trend was the same: winter > spring > autumn > summer. The Margalef richness index R ranged from 2.28 to 3.17. The variation range of Shannon-Wiener diversity index H'_N and Pielou evenness index J'_N based on individual number was 1.24-2.14 and 0.14-0.34, respectively. The variation range of Shannon-Wiener diversity index H'_W and Pielou evenness index J'_W based on biomass was 1.64-2.51 and 0.21-0.49, respectively. All indexes were significantly higher in summer than those in other seasons, except H'_W in summer and autumn (P<0.05). The results showed that the fish species diversity of the Shijiu Lake were low. This study complements the basic data of fish community research in the Yangtze River-connected lake, and has a certain significance for the protection of fish diversity in the middle and lower reaches of the Yangtze River.