Dumped sediment transport at the dredge disposal site in the north passage of the Yangtze estuary is studied by field measurement. The volume of dredge disposal zone is obtained by multi-beam sonar. The density of surface is measured by sampler-collection and the density of different level is measured by stationary-piston sampler. The sediment loss ratio from the disposal zone can be calculated by the volume of dredge disposal zone and the total disposal dredge of the self-propelled trailing suction hopper dredgers. The result shows that the sediment loss ratio is about 76%. The flow velocity obtained by flow-measure- system is so big that much sediment can be carried out of the disposal zone, which can be used to explain the sediment loss ratio. The location of dredge disposal zone should be moved to the middle section of dams for reducing the sediment loss ration.