Based on the previous research on the classification criteria of different coasts,we carry out an in-depth research on the classification criteria of muddy and silty coasts according to the hydraulic experiment of sediment with clay content between 15% and 25%.It is shown that coasts with median diameter greater than 0.10 mm and clay content no better than 0% are defined as the sandy coast.The coasts with median diameter between 0.03 mm and 0.10 mm and clay content less than 10% are defined as the silty coasts.The coasts with median diameter less than 0.03 mm and clay content greater than or equal to 25% are defined as the muddy coasts,and that clay content ranging from 10% to 25% are defined as transition zone between muddy and silty coasts.The results provide a new case study for the application of the domestic and foreign research on the coastal engineering of the muddy coast.