Abstract: With the development of the 12.5 m deep-water channel of the Yangtze River estuary,the deep water channel extending up to Nanjing is in urgent need.The start-up year of the existing datum of Nanjing downstream is 1970.In the study,the navigation datum upstream of Jiangyin has been adopted,and the theoretical datum downstream of Jiangyin has been used.With the human activities such as river channel regulations and bridge construction and the natural factors such as sea level rise,the tidal wave from Nanjing downstream has been transformed along distance,the existing datum needs to be recalculated and rechecked.In this paper,tide data of different stations along distance has been collected,interpolated,extended and completed by one dimensional mathematical model.Based on these tide level data,we calculated the datum plane of Nanjing downstream by use of integrated cumulative curve method,and compared the difference between existing datum planes and our calculation datum planes.It is shown that the existing datum planes can ensure ship navigation safety,and that the charts,topographic maps and relevant research results based on the existing datum are reliable and applicable.