Abstract: The sediment particle size composition is a clear indicator of sedimentation, sedimentary environment, and sedimentary dynamic conditions. In order to understand the sedimentary characteristics of the outer bay waters of Qinzhou Bay in Guangxi, 167 sets of surface sediment samples were measured for particle size, and analyzed for particle size parameter characteristics to divide the sediment types. The Pejrup triangle map was used for the partition of the sedimentary dynamic environment of the outer bay waters of Qinzhou Bay, and Gao-Collins particle size trend analysis method was used to summarize the migration trend of surface sediments in the study area. The results show that the surface sediments in the outer bay waters of Qinzhou Bay is mainly composed of silt and sand, with poor sorting ability. According to the Folk-Ward classification method, the authors divided the surface sediments in the outer bay waters of Qinzhou Bay into 12 types, and sandy silt, sandy mud and silt were the most widely distributed, accounting for 22.16%, 17.37%, and 14.97% of the total sample size, respectively. The analysis of sedimentary dynamics indicates that the sedimentary environment in the study area is complex, and the hydrodynamic forces is strong, which are generally characterized by a gradual weakening outward from the bay mouth. The trend analysis of particle size indicates that the sediment in the study area migrates towards the bay mouth and tidal deep channel (channel) as a whole. Comprehensive analysis shows that the sedimentary environment in the study area is mainly influenced by tidal currents, waves, and human activities. The research results could provide scientific references for port construction and the expansion of deepwater waterways.