Abstract: The grain size analysis of 40 surface sediments collected in the adjacent sea area of Tianjin Nangang Industrial Zone was analyzed. The results show that most of the sampling sites in the study area are clayey silt. Only three sampling sites are silt and one sampling site is sandy silt. According to the features of sediment grain size parameters, the study area can be divided into 3 groups that belong to 3 different depositional environments. In group I, the sediment average grain size is relatively large with high content of sand in the sediments where the hydrodynamic force is low and medium. Further, the sediment grain size and the location of sea area can be divided into two depositional environments according to the relative weak influences of river. That is the sedimentary environment under the influence of multiple dynamics (I-1) and the sedimentary environment (I-2) affected strongly by the smaller tides and weakly affected by the river. In group II , the sedimentary environment in the subtidal zone is influenced by the hydrodynamic forces of the strong river and the tidal current hydrodynamics. In Group III, The sediments grain sizes are coarse sands and the hydrodynamic environment is relatively stable, which affects the sedimentary environment of the seasonal bay circulation. In addition, the intertidal zone in the southwest bank of the study area turned to the northeast, with the sediment grain size becoming smaller. The reason is that the coarsegrained matter was carried to the intertidal zone by the river in the southwest bank, Under the joint action of rivers and coastal currents, they run northwards and are blocked by Nangang Industrial Zone. Deposits of coarse sediments, fine-grained particles flow back to the south with the rebound of the water flow and then move to the northeast direction under the current of northward movement, resulting in the sediment particles of the sea area thinning.