In order to characterize the species diversity of nekton communities and their seasonal change, we collected catch and environmental data of the survey in Haizhou Bay in April and September, 2022, in this study. We analyzed the spatiotemporal pattern of Margalef species richness index, Pielou evenness index, Shannon-Wiener diversity index and Simpson diversity index. The generalized additive models (GAMs) were used to analyze the relationships between these indices and environmental factors. Our findings showed that the spatial patterns of the indices were relatively consistent in spring, higher in the southern Haizhou Bay, the waters around Rizhao offshore, Qiansan islands, and lower in the northeastern Haizhou Bay. There were obvious differences among indices in autumn; the Margalef species richness index was higher in the northern and southern areas and lower in the central area while the remaining indices varied with latitude. Except for Margalef species richness index, all other indices were higher in autumn than in spring. The GAMs revealed that the indices were mainly influenced by water depth and bottom temperature in spring, and by bottom salinity and water depth in autumn. The environmental factors affecting the these indices and their contribution rates varied among seasons, and among indices in the same season. Our findings should aid to the biodiversity conservation and fishery management in Haizhou Bay.