利用σ坐标系下的斜压浅海环流模式，研究M2分潮对夏季长江冲淡水扩展的影响。在“准定常流”作用下，模拟出能反映夏季长江冲淡水扩展的盐度场，并模拟出与黄、东海实测资料相符的M2分潮。在此基础上，用两种方案讨论M2分潮对冲淡水的影响。第一种方案，仅考虑M2分潮，计算它对冲淡水扩展的影响。第二种方案，将M2分潮和“准定常流”耦合，计算冲淡水扩展的变化。结果表明，从分潮对冲淡水扩展有一定影响，其中包括潮混合和定向输运。 Using the baroclinic shallow sea circulation model in the σ coordinate system, the effects of M2 tide on the expansion of summer Yangtze River freshwater were studied. Under the action of “quasi-steady flow”, the salinity field which can reflect the extension of the summer Yangtze River freshwater is simulated and the M2 tide corresponding to the observed data of the Yellow Sea and the East China Sea is simulated. On this basis, two schemes were used to discuss the impact of M2 tidal dilution on freshwater. The first solution, considering only the M2 tide, calculates its impact on the expansion of freshwater. The second option, the M2 tide and “quasi-constant flow” coupled to calculate the changes in the dilution of water. The results show that there is a certain influence from the moisture diversion and denudation of freshwater, including tidal mixing and directional transport.