It is apparent that there is a difference between mud coasts and sand coasts in such aspects as sediment components, hydrodynamics of nearshore waters, and the formative process in configuration, and profile. The intensity distribution of waves affecting the mud flats in Lianyungang, and the conditions determining tidal water levels, are discussed in this paper. A mathematical model which describes the erosion process of mud flats has been derived on the basis of the results of tests for the mud process in seawater. The model is satisfactory for the actual mud flat profile change in Lianyungang with artificial mud discharges.