Abstract: To elucidate the distribution characteristics and transport mechanisms of surface sediments in the northeastern Beibu Gulf and western mouth of Qiongzhou Strait, sediment samples from 339 stations were used and the compositions, types, grain-size parameters, and spatial distribution characteristics were systematically analyzed. The Gao-Collins grain-size trend analysis (GSTA) model was applied to investigate the sedimentary dynamic processes in the study area. Results show that the mean grain size of surface sediments showed a spatial variation from coarse grain to fine grain from east to west, and sand, silt, and clay components formed significant transition zones near the 20-m isobath. Sediment types were dominated by sandy mud, while muddy sand and silty sand were primarily distributed in the western mouth of Qiongzhou Strait. The Flemming triangle diagram indicates that the study area represents a moderate to high-energy sedimentary environment overall, and the western mouth of Qiongzhou Strait was characterized by high-energy conditions, while the northwestern area by moderate to low-energy conditions, and the 20-m isobath served as an important sedimentary dynamic boundary. Sediment transport trends show distinct east-west differentiation, northwesternward or northward transports in the western deep-water area, complex transport patterns with convergence centers in the eastern shallow-water area, and an obvious transition zone in the central area. The sediment distribution and transport patterns were primarily controlled by the multiple factors of the venturi effect at Qiongzhou Strait, Beibu Gulf circulation, and tidal delta topography. This study provided a scientific basis for understanding the evolution of sedimentary environments in this region and an important reference for coastal engineering construction, channel planning, and marine resource development.