To explore the characteristics and diversity of fish communities in the waters south of the Nanri Island, three comprehensive surveys of fishery resources were conducted in the winter of 2009 and the spring and summer of 2010. Bray-Curtis cluster was used to classify the fish communities in the surveyed area, and the number of species, density, ecological groups, and diversity of fish species were analyzed on the basis of the division of fish communities. The effects of the changes in water masses on fish communities' classification and diversity were discussed in detail. The results indicate that in spring, the fish communities comprise two different groups: the northern coastal community and the southern nearshore community. The number of species, density, and the individual diversity index (H') of the northern coastal community were 27 species, 7.47 × 10³ individuals/km², and 2.71, respectively, and the corresponding values of the southern nearshore community were 32 species, 24.34 × 10³ individuals/km^2, and 1.97, respectively. The number of species and density of warm water species of the southern offshore community were higher than the corresponding values of the northern offshore community. In contrast, the warm temperate species exhibited the opposite scenario-0. In summer,the number of species, density, and H' of the western coastal community were 55 species, 329.24 × 10³ individuals/km², and 1.97, respectively, while the respective values of the eastern nearshore community were 27 species, 106.47 × 10³ individuals/km², and 1.62, respectively. The individual density of both coastal species and nearshore species of the western coastal communities were higher than those of the eastern nearshore community. In winter, the fish communities were divided into northern coastal community and southern nearshore community. The number of species, density, and H' in the northern coastal community were 25, 9.96 × 10³ individuals/km², and 2.71, whereas the corresponding values in the southern nearshore community were 32 species, 28.85 × 10³ individuals/km², and 1.97, respectively. The individual density of warm water species and warm temperate species in the southern coastal community were higher than those in the northern nearshore community. In winter and spring, the number of fish species, individual density, and diversity, of the warm water species in the area controlled by the Taiwan Strait warm waters were higher than those of the species dominated in the Fujian-Zhejiang coastal waters. In summer, with the influence of the Taiwan Strait warm water and overland runoff, the corresponding values of the fish community in the western region of the study area were higher than those in the eastern region. We conclude that the demarcation and characteristics of the fish communities were closely related to the seasonal changes of water masses.