Abstract: For estuaries of big rivers with large water depth and heavy traffic, it is impossible to carry out traditional six-layer sampling measurement for sediment concentration.How to obtain more accurate vertical average sediment concentration and improve the measurement accuracy of sediment flux into the sea is the focus of current scholars.Taking the Xuliujing hydrological corss-section as an example, a key node of the Yangtze River Estuary, the average sediment concentration of the vertical line was calculated by a variety of hierarchical combination methods, and the confidence interval, average relative error and Lilliefors hypothesis test were used for calculation and analysis.At the same time, combined with the upstream and downstream hydrological corss-sections data of the observation node, the characterization law of the vertical average sediment concentration representative layer was preliminarily clarified.It was found that although the Xuliujing hydrological cross-section is affected by the runoff-tide interaction, the 0.6H layer was proved to be the best representative layer, and the average relative error of the observation results was in the range of(0±5)%.However, in the south branch of the lower reaches, the hydrological cross-section of Baimaosha was significantly affected by tidal dynamics, resulting in poor representation of 0.6H single layer.The research results have important guiding significance for the future transformation of hydrological integrated buoys and the accurate acquisition of sediment flux from the Changjiang River to the sea.