During June 9th to 15th in 2017, the dynamic of Gymnodinium catenatum bloom along the coast of Hui’an County Fujian Province, were investigated. Six monitoring stations were established for marine environmental factors assessment over seven sampling trips. The water quality data from June 6th, along with the phytoplankton data collected in March and November 2017, was selected for comparative analysis. Furthermore, the survey results of dinoflagellate cysts and paralytic shellfish poison (PSP) in cultured shellfish were integrated to explore the relationship between dormant cysts and the bloom dynamics, as well as the patterns of PSP accumulation and elimination in cultured shellfish. The results revealed that during the bloom, conditions were characterized by sunny weather and favorable sea states, with water temperature ranging from 24.2℃ to 26.8℃ and the salinity between 30.4 and 33.2. The concentrations of nutrients were low, indicating oligotrophic conditions, while the density of G. catenatum peaked at 1.79×10⁶ cells/L during the bloom period. The interplay of favorable hydro-meteorological conditions, N/P ratio and the trophic pattern of G. catenatum provided a basis for the evolution of the bloom, whereas adverse weather conditions primarily contributed to its decline. The average density of G. catenatum cysts in the surveyed sea area was 33.2 cysts/g, suggesting potential for these cysts to germinate into trophic cells, which could lead to the reemergence of the bloom and therefore it necessitates further attention. During the bloom period, both oysters and mussels rapidly accumulated high concentrations of PSP toxins, with levels directly proportional to G. catenatum density. Additionally, even low densities of G. catenatum posed a risk for PSP exceedances. Mussels exhibited a rapid accumulation and slow elimination of PSP, with a significantly greater capacity for toxin accumulation compared to oysters, while their elimination rate was significantly slower.