During the construction of the third stage of Improvement Project of Deep-water Channel of the Yangtze estuary, 6 ADCP hydrologic survey vessels were arranged to measure the diffusion condition of the suspended sediment via fixed synchronous cross section measurements, which was carried out in China for the first time. The result of suspended sediment diffusion field was observed when the dredged sediment was overflowed during dredging in channel and deposited in the disposal area in the north passage of the Yangtze Estuary during the tidal fluctuation period. According to that, the optimized construction method was improved.