Abstract: Shangchuan Island and Xiachuan Island are two of the biggest islands along the coast of western Guangdong province,China.The faults in these two islands are divided into two sets,NE and NW trends,controling the development of the landforms.There are five-step landform surfaces:270-350m, 170-200m, 120-150m,50-60m and 0-5m.The step-landform is the evidence of regional crust intermittence elevating.The landforms of the two islands can be classified into 14 types,consisting of granite and metamorphic rock as well as Quaternary sediment.According to the data of C¹⁴ ages,strata,geological structure and sporopollen analysis,we deduce that these two islands were separated from the continent in the Middle Holocene(Q₄²) by the transgression. Dated by C¹⁴ method, the age of the lagoon plain shell muck sample(buried depth 1.5m) is 2780±90 yrs B.P.,which shows that the lagoon plain has been forming since the Late Holoceae(Q₄³).