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建立一个σ坐标系下三维非线性斜压浅海与陆架模式，并首次应用于长江冲淡水扩展机制的研究。考虑实际海岸形状和海底地形，在空间完全交错的网格系统上，离散化控制方程组，采用ADI计算方法数值求解。数值试验结果首次表明，在夏季长江口水位向外倾斜，冲淡水穿越等水位线运动，远离长江口水位倾向东北，冲淡水沿水位坡面运动，同时再现了伸向东北的冲淡水舌和东海陆架上的环流结构。夏季苏北沿岸流作为长江口北部海区的一股势力，阻挡了长江冲淡水沿岸北上，并使之东转。苏北沿岸流强，冲淡水不易北上，反之，北上加深。它是决定夏季长江冲淡水总的分布形态中一个不可缺少的外在因素。
A three-dimensional non-linear baroclinic shallow-sea and shelf model in σ-coordinate system was established and applied for the first time to research on the mechanism of Yangtze River red water expansion. Considering the actual coast shape and the seafloor topography, on the grid system with complete space staggered, the governing equations of discretization are numerically solved by ADI method. The numerical results show for the first time that in the summer, the water level of the Yangtze Estuary slopes outward and the fresh water passes through the water level. The water level away from the Yangtze River mouth tends to the northeast and the flushing water moves along the slope of the water level. Meanwhile, the red water tongue and the East China Sea Circulation structure on the shelf. As a force in the northern sea area of the Yangtze Estuary, the flow of the northern Jiangsu coast in the summer prevented the Yangtze River’s red water from going northward along the coast and turning it eastward. Strong flow along the coast of northern Jiangsu, red water is not easy north, on the contrary, deepening north. It is an indispensable external factor in determining the total distribution pattern of summer red water in the Yangtze River.