The comparison of the terrain data from the past 40 years shows that the inlet of the Xiaomiao-hong 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.%近40年来地形资料对比显示,小庙洪水道口门段存在北淤南冲的演变趋势,口门段北水道深槽不断萎缩直至消失,南水道则充分发展.通过对实测水文资料分析和所建立的潮流数学模型,从动力的角度阐述了小庙洪口门各水道多年来冲淤变化的机制.研究表明小庙洪水道是受潮流控制为主的潮汐水道,水道近年来之所以表现出南冲北淤的状态,与口门水道内部潮流的性质有很大的相关性.北水道呈涨潮水道性质,中、南水道表现出落潮水道性质.南、中水道断面输沙量为净泄,北水道断面为净进,水道口门段悬沙存在“北进南出”趋势,悬沙运移的趋势与近几十年来小庙水道北水道淤积、萎缩；南水道冲刷、发展的态势相符合.
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