The South China Sea (in short the SCS) possesses of three tectonic units: continental shelf, continental slope and ocean crust. The sedimentary basins are mainly located in the continental shelf and the continental slope. In the SCS, hundreds hydrocarbon fields have been discovered so far. Those hydrocarbon fields character as the outside-oil and the inside-gas. The oil fields locate mainly in the continental shelf or the area near the land. The gas fields locate mainly in the continental slope or the area near the ocean. In the sags which located in the outside-oil belts, the middle-deep lake face mud and Ⅰ&Ⅱ₁ types kerogen are dominated in the source rocks. The source rocks produce mainly the crude oil.