Abstract: The broad offshore is very rich in oil-gas resources in China. Amounts of oil and gas were discovered in this area during 40 years of exploration. However, owing to the limitation of technology, information and research extent, it has always been considered that all the basins in China offshore are similar in types and geologic conditions and classified as the Cenozoic rift basins on the continental margin. The analysis on a massive amount of seismic and drilling data shows that there are two depression belts in China offshore. The two depression belts are evidently different from each other in their tectonic situations, geothermal gradients, basin types, forming periods, sedimentary environments, petroleum geologic conditions and petroleum properties. The first depression belt containing Bohai Bay Basin, South Yellow Sea Basin, Taibei Depression, ZhuⅠ Depression, Zhu Ⅲ Depression and Beibuwan Basin is the lacustrine rift basin located on the continental crust and mainly generates oil. The second depression belt containing Zhedong Depression, Zhu Ⅱ Depression, Qiongdongnan Basin and Yinggehai Basin belongs to the marine depression basin located on the continent-to-ocean transitional crust and mainly generates gas. The first depression belt has already become a very important oil-producing area, and the second depression belt is expected to be a large gas-producing area in China offshore.