Tidal flow mathematical model is used to calculate the dominant discharge and to investigate characteristics and changing rules of the tidal reach from Datong to the Yangtze River estuary.The results show that the flow sediment transport rate method is convenient and the calculation result is reasonable when applied to the tidal reach.There are two dominant discharges for the reach above Tianshenggang,while there is a flow group for the lower reach of Xulujing.The dominant discharge changes little along the way from Datong to Yizheng,and then gradually increases along the way from Yizheng.It should be mainly related to the increase of the tidal prism along the way.