The waters of the Yangtze River estuary are characterised by a large number of channels and complex changes in river conditions.To analyse the changes in hydrology of the south channels and north passage of the Yangtze River estuary under the action of runoff currents，and further improve the understanding of the south channels and north passage of the Yangtze River estuary，statistical comparative analyses are conducted on the hydrological characteristics based on the hydrographic data of the flood and dry season at each measured station in the Yangtze River estuary from 2018 to 2022.The research results show that the impact of runoff and tidal current changes on the hydrological features of the south channels and north passage of the Yangtze River estuary are different，and the upward and downward flows of the waters are influenced by the coupling effect of runoff and tidal current at the same time.The critical point of the influence of the runoff tide in the south channels and north passage is around the upper mouth of the north passage.The critical position oscillates with the change of the runoff and tide，and the position of the salt water wedge and the maximum turbidity zone also oscillates up and down with the change of the runoff and tide.This oscillation also causes the change of the silt return distribution.