Based on the data obtained from ocean drilling wells and the seismic profile data, differences and changes in sediment sources of the deep-sea basin in the South China Sea (SCS) during syn- and post-seafloor spreading are determined quantitatively. It is shown that the oceanic basin of the SCS started to be formed as far back as the Oligocene (32Ma), and it extends with two spreading events of the SCS. The basin is mainly filled with volcanic conglomerate and ash, carbonate rock, ultra-microfossil mud, muddy clay, silty clay, mudstone and silt-fine grained sandstone. The main sediments in the deep-sea basins are terrigenous deposits since the Late Miocene (11.6Ma). The supply of plentiful terrigenous deposits is closely related to the regional tectonic events (such as the rapid uplift of the Qinghai-Tibet Plateau and the subduction of the Philippine plate) during the closing process of the SCS, as well as the strengthening of the East Asian monsoon since the Late Miocene and the strong weathering and erosion of the source area.