On the basis of comparative analysis of foraminiferal assemblages zones for Holes XL1, XL2 and CY, integrating the characteristics of their aggradation and environmental magnetism, the authors probe into the evolvement of the deposit hydrodynamic condition in the North Branch, the Yangtze River Estuary. At the same time, it reveals the relation of sedimentary facies corresponding to their foraminiferal assemblages zones. Based on foraminiferal assemblages zones, magnetic properties and lithofacies, the authors also suggest that there are three modes of sedimentary environment for Hole XL1, XL2 and CY in the North Branch estuary, the Yangtze River Esturary: tidal current ridge→tidal channel→supratidal zone, forming the sedimentary facial sequence of the filled estuary.