Based on investigations of the new high resolution gravity and magnetic data, combined with swath bathymetry, the Cenozoic evolution model of the South China Sea is revisied. Two major sea-floor spreading stages were revealed with different dynamic mechanisms, separated by a remarkable tectonic-sedimentary event near 25 Ma. Different tectonic areas developed during these two spreading episodes in the oceanic basin. The whole oceanic basin could be divided into three subregions from north to south. Before the collision of the Luzon arc with and Eurasia Plate, the South China Sea was a gulf-shape marginal sea opening to the Pacific Ocean, resulting from westward propagation of a spreading center inside the Sunda Continent, as in the case of the western Gulf of Aden.