By comparing the sediment properties and transporting laws in different branches of the Changjiang estuary,it is concluded that sediment input in the estuary is in tremendous quantity.The asymmetry in tidal ebb and flood currents and the gravitational circulation are the majormechanisms of concentrating sediments around the null Eularian residual current point and of generating the turbidity maximum.The turbidity maximum is characterized by high sedimentsconcentration and high flocculation rates.Under strong tidal current bottom sediments are massively resuspended,strengthening sediments transprotation.The excursion area of the turbiditymaximum approximately consists with the mouth bar area.The present study has practical meaning in furthering our knowledge of the generation and evolution of the mouth bars.