Abstract: A new method simulating the movement of dumped silt in open estuarine waters is developed and the movement process of dumped silt in the surrounding water body of Macao is numerically calculated by using a distributed point source diffusion model and a 2 D visco sediment mathematical model. Results show that the silt mainly deposits in a small scope around the dumping point and the heavy deposition is not corresponding to the dumping point because of the influences of tidal current.