The range of relative sea level rise in the northwestern South China Sea since the Last Glacial Maximum was over 100 m. As a result, lowland regions including the Northeast Vietnam coast, Beibu Gulf, and South China coast experienced an evolution from land to sea. Based on the principle of reconstructing paleogeography and using recent digital elevation model, relative sea level curves, and sediment accumulation data, this paper presents a series of paleogeographic scenarios back to 20 cal. ka BP for the northwestern South China Sea. The scenarios demonstrate the entire process of coastline changes for the area of interest. During the late glacial period from 20 to 15 cal. ka BP, coastline slowly retreated, causing a land loss of only 1×10 4 km 2 , and thus the land-sea distribution remained nearly unchanged. Later in 15-10 cal. ka BP coastline rapidly retreated and area of land loss was up to 24×10 4 km 2 , causing lowlands around Northeast Vietnam and South China soon to be underwater. Coastline retreat continued quite rapidly during the early Holocene. From 10 to 6 cal. ka BP land area had decreased by 9×10 4 km 2 , and during that process the Qiongzhou Strait completely opened up. Since the mid Holocene, main controls on coastline change are from vertical crustal movements and sedimentation. Transgression was surpassed by regression, resulting in a land accretion of about 10×10 4 km 2 .relative sea level change, paleocoastline reconstruction, Last Glacial Maximum, northwestern South China Sea Coastline changes are forced commonly by climatical eustasy, crustal deformation, sedimentation or erosion, and human activities, among which eustasy and crustal deformation are the major factors leading to global or regional coastline changes. Since the Last Glacial Maximum (LGM), coastlines all over the world have changed dramatically as the sea level rose from more than 100 m below to the present level. Lowlands in the northwestern South China Sea even experienced a transition from land to sea. Therefore, sea level change since the LGM had a significant impact on the global land-sea distribution, and global or regional paleoshoreline reconstructions will provide insights for the studies of paleogeographic evolution and human migrations [1] . For example, paleoshoreline reconstructions of the Persian Gulf have implications for models of the evolution of the Euphrates-Tigris-Karun delta, as well as for the timing of people's first settlements in lower Mesopotamia [2] .Based on coastline reconstruction principles [3][4][5] , we attempt to model the shoreline change process since the LGM for the northwestern South China Sea (105°E-116°E, 14°N-25°N), using recent digital elevation model, relative sea level curves, and data of sediment thickness, in order to better understand the evolution of land-sea distribution. A successful application of the
