Abstract: Oil and gas exploration activities in the Yinggehai and Qiongdongnan Basins of northern South China Sea have lasted for more than 30 years. The oil and gas fields found there are mainly belong to structural type of hydrocarbon reservoir. To meet the needs in exploration, it is required to look for non-structural subtle trap of oil and gas reservoirs. The Yinggehai and Qiongdongnan Basins of the northern South China Sea have favorable conditions for the formation of subtle traps:there are plenty of hydrocabon source in the Yinggehai and Qiongdongnan Basins and frequent sea level changes in history. Shifting of lithological belts helps the formation of lithologic reservoirs. The basin bottom and slope fan systems formed as part of the low-stand system tract in the low-water level period are well developed. In addition, there are frequent tectonic activities in history, which are favorable for the formation of stratigraphic-unconformity traps.