Abstract: A three-dimensional numerical model was established to assess the impacts of a cross-shore groin on the suspended matter dispersal off the Yellow River Mouth. The numerical results indicate that the groin cuts off the pathway of long-shore sediment transport off the present Yellow River Mouth, prevent the river sediment dispersing southward and result in rapid sediment accumulation in the south of the river mouth. Meanwhile, the abandoned Qingshuigou River Mouth was subjected to serious erosion due the cutting off of the sediment supply from the present river mouth. The numerical results fit the changes of shoreline from 2000 to 2013 as acquired from the LANDSAT imageries.