Abstract: Based on environmental survey data from the waters of Hebao Island, Zhuhai, this study constructs a Habitat Suitability Index (HSI) model based on trapezoidal fuzzy membership to explore the spatiotemporal evolution patterns of habitat suitability for Crassostrea hongkongensis. This aims to provide data support and a technical system reference for the spatial planning of species and the scientific management of comprehensive aquaculture models in the island and reef waters of the South China Sea. This study quantified the spatiotemporal evolution characteristics of habitat suitability for the Hong Kong oyster, a typical economic species in the waters of Hebao Island, Zhuhai. Taking Hebao Island and its adjacent waters in the northern South China Sea as the study area, and based on measured marine environmental data from four cruises conducted from 2024 to 2025, eight core parameters (water depth, water temperature, salinity, dissolved oxygen, chlorophyll-a, ammonia nitrogen, nitrite, and nitrate) were selected through a multicollinearity test. Using a trapezoidal fuzzy membership function and the Analytic Hierarchy Process (AHP), a comprehensive HSI model was constructed based on a Weighted Linear Combination (WLC). Salinity (weight 15.2%) and water temperature (weight 14.5%) were the absolute dominant factors determining the habitat suitability for C. hongkongensis in this marine area. In spring, 100% of the waters were in a highly suitable state (HSI > 0.8); during summer and winter, the entire region generally maintained a good suitability level (0.6 ≤ HSI < 0.8). However, in autumn, habitat suitability experienced a large-scale degradation where the optimal suitability zone disappeared, and 12.7% of the waters dropped to a moderately suitable level (0.4 ≤ HSI < 0.6). Overall, the habitat suitability in the study area exhibited extremely high spatial heterogeneity, generally presenting a spatial pattern of "superior in the deep-water areas of the northwest and inferior in the shallow-water areas of the southeast." On a temporal scale, it demonstrated an evolutionary pattern of being "optimal in spring, maintained in summer and winter, and degraded in autumn." The model can effectively reflect the seasonal habitat characteristics of C. hongkongensis and explore the spatiotemporal evolution patterns of its habitat suitability. It provides data support and a technical system reference for the spatial planning of species and the scientific management of comprehensive aquaculture models in the island and reef waters of the South China Sea.