Abstract: Through comprehensive analysis of the basin nature (basement property, deep structure and basin types), sedimentary-structural characteristics (tectonic units features, tectonic evolution stages,sedimentary characteristics and deposition-subsidence rate), and petroleum geological characteristics(source rocks characteristics, trap types, source-reservoir-caprock assemblages and hydrocarbon reservoir types) of the main offshore oil and gas bearing basins in China (the Bohai Bay basin, the East China Sea shelf basin, the Pearl river mouth basin, the Beibu gulf basin, the Yinggehai basin and the Qiongdongnan basin),the formation mechanism of these basins has been discussed in this paper. It is believed through study that these basins are similar in basement property, being steady rigid continental basement. The deep structures are coupled with macroscopical structural forms. The development of these basins is controlled obviously by faults, and the tectonic evolution history is similar. The deposition-subsidence center shifted in similar ways. Several sets of source rocks are well developed, and there are many sets of source-reservoir-caprock assemblages, with structural traps dominated.