Based on four natural sandy beaches in Lianyungang muddy coast,this study analyzes the morphological characteristics of beach plane and profile,tidal current conditions,wave conditions and sediment movement characteristics to study the reasons for the existence of sandy beaches in muddy coast environment.The results show that the natural beaches are concave arc-shaped landforms with headlands at both ends,and the main direction of the incoming waves is consistent with the direction of the bay mouth,which is not conducive to significant coastal sediment transport and avoids sediment loss.The natural beach profile has obvious turning characteristics,and the larger front water depth is conducive to reducing loss during the propagation of offshore waves,which can maintain larger wave dynamic conditions in front of the beach.The large waves in the direction of the natural beach should reach a certain concentration and frequency,and the large waves of the beach with H1/10 wave height greater than 0.40 m accounting for more than 36.6% is conducive to better beach surface characteristics.Waves are the main driving force of the mud resuspension.The sand carrying capacity of the tidal current is greater than the background sand concentration,which is conducive to the formation of the beach,and the larger the sand carrying capacity,the wider the beach width.