The mechanism decomposition method is used for calculating the water and sediment date, the sediment flux has been divided into 8 dynamic items, the characteristics of the suspended sediment transport have been illustrated through exploring the mechanism of the advection, tidal pumping effects and the vertical circulation for sediment transport. The results show: in the year of the hydrological data measured, most of the suspended sediment in the North Passage of the Yangtze River Estuary comes from the upstream regions. The advection is the main factor to affect the suspended sediment transport. The tidal pumping effect plays a minor role. In the channel, the vertical circulation for sediment transport is mainly controlled by the Euler residual flow. The vertical sediment concentration changes significantly in the deeper region, the residual current directions are inconsistent in different vertical layers in the shallow estuary region, the vertical circulation plays a stronger role in the shallow regions.