This paper analysed the main factors of the coastal formation in South China, i.e. the geological structures, the geographical conditions of the mainland coast, the raise of the sea-level during Holocene, the tide, the wave, the longshore drift and so on. The coast in South China is characterized by the pattern of barrier-lagoon (or bay), because the tide range is small and the sediment transported by wave is rather strong. The mud-sand of most part of the barriers was derived from inner shelf, and moved landward with sea-level rise in Holocene. The author described in full details of the morphology about the two patterns of harbour-coasts (i. e. sub-merged valley and barrier-lagoon) The characteristics of the harbour of barrier-dagoon are as follows: 1. A harbour with the ha rrier-lagoon is commonly independent from the adjacent coastai systems; 2. Either the pluvial-alluvial terraces and the erosion platforms or the hills always lie at the back of the harrier-lagoon (or bay) systems; 3. During the Holocene, the barriers had evolved continuously by retreat, progradation and return. That correspondingly caused the changes of the other morphology, such as the area of lagoon. the mud flat, the tidal inlet and its sand bodies; 4. The foreshorelines of most barriers have tended to the logarithmic spiral plan shape; 5. The morphodynamics of beach may be divided into three sections; 6. The throat-position of the tidal inlet is always situated in the apexof Z-shaped headl-and-bay and is generally stable.