The comparison of the terrain data from the past 40 years shows that the inlet of the Xiaomiaohong channel has an evolutionary tendency of deposition in the north and erosion in the south. The north trough was silted constantly to disappear while the south trough developed adequately. The hydrodynamic mechanism of the change in deposition and erosion in different channels was discussed based on the analysis of field data and the tidal current Mathematical model. The reason that a state of deposition in the north and erosion in the south exists in the Xiaomiaohong channel during the past years is closely related to the tidal current characteristics in this area. The ebb flow discharge is stronger than flood in the south and middle waterways of the inlet, with an “ebb-dominated” style. On the contrary, the north waterway has a “flood-dominated” style. The sediment transportation shows a trend of northward inflow and southward outflow, consistent with the trend of deposition and atrophy in the north waterway and erosion and extension in the south waterway.