Macrobenthic species are pivotal in aquatic ecosystems, as they play indispensable roles in maintaining ecological balance, biodiversity, and energy cycling. In-depth studies of the dominant species among large benthic animals can significantly enhance our comprehension of the structure and function of benthic ecosystems. This knowledge not only furnishes a scientific foundation but also offers strategies for ecological conservation, environmental management, and sustainable resource utilization, consequently fostering the health and stability of ecosystems. In order to explore the distribution characteristics and community assembly mechanisms of dominant macrobenthic species in mussel culture areas, this study utilized survey data on macrobenthic species from the mussel culture area of Gouqi Island, Shengsi. The data were collected in spring (April), summer (August), autumn (November) of 2021, and winter (January) of 2022. Various methods, including diversity indices, the Raup-Crick index, the diffusion-niche continuum index (DNCI), mantel analysis, principal coordinates of neighbor matrices, and variation partitioning analysis, were employed to investigate the relationships between the diversity distribution of dominant taxa and environmental and spatial factors, as well as the community assembly mechanisms. A total of 195 macrobenthic species were identified, with 42 dominant species selected for study. Polychaeta constituted the largest proportion (76.2%), followed by Malacostraca (7.1%). Sternaspis scutata, Amphioplus japonicus, and Heteromastus filiformis were the dominant species observed across all seasons. The temporal and spatial variations in diversity indices were significant (0.63-2.39), with the overall diversity of dominant taxa being higher inside the aquaculture area than in the periphery. The average diversity was highest in summer and lowest in winter. Nitrate, nitrite, dissolved oxygen, water temperature, and offshore distance were identified as key environmental factors influencing the distribution of dominant macrobenthic species. The distribution and diversity of dominant species were significantly affected by environmental filtering. The assembly of dominant macrobenthic species' communities was influenced by a combination of stochastic and deterministic processes. In autumn, the roles of stochastic and deterministic processes in community formation were relatively balanced, while deterministic ecological processes, such as environmental filtering, played a dominant role in community assembly in spring and winter. Community assembly in summer was more influenced by stochastic processes. Further analysis revealed that both diffusion processes and niche processes jointly dominated the community assembly of dominant taxa, with diffusion processes having a greater impact on community assembly than niche processes. The results of this study provide a reference for the ecological evaluation of mussel culture activities and their carrying capacity management.