Abstract: The Tangdao Bay is a narrow and semi-enclosed one with complex hydrodynamic conditions. Samples were collected in the intertidal zone at fixed sites and times. We discussed the depositional characteristics and hydrodynamic conditions of the sediments in this paper based on grain size data. The sediments in this area are mainly composed of silty sand with poor sorting, positive skewness and wide kurtosis. Probability cumulative curves show that the deposits are dominated by the type of sediments with two saltation peaks and one suspension peak. Combined with the grain size-standard deviation curves, it is concluded that the environmentally sensitive grain-size components <158.6 μm are basically influenced by tidal currents, whereas the sediments between 158.6~369.1 μm and >369.1 μm respectively are contributed by waves and storm waves. By the study of the components <158.6 μm, the monthly tidal cyclicity can be easily recognized. Finally, it is carried out the study of the deposition of tidal deposits, changes in tidal creek and erosion and/or siltation of the tidal deposits of the research area, so as to better understand the hydrodynamic conditions in a semi-enclosed and narrow bay as such and the protection of coastal zones.