Abstract: The deep-water area of Qiongdongnan Basin has abundant oil and gas resources. A giant gas fi eld with resources of over 100 billion cubic meters has been discovered in Ledong-Lingshui Sag in the western deep-water area. While no breakthrough has been made in Baodao- Changchang Sag in the eastern deep-water area due to the great burial depth, poor reservoir physical properties and poor understanding of hydrocarbon accumulation conditions. Recently, a risk exploration Well BD21, located at the northern fault terrace zone in Baodao Sag, obtained high-yield condensate oil and gas production of 200.2m³/d and 73.12×10⁴m³/d in the 3rd member of Lingshui Formation, which was a remarkable breakthrough in the eastern deep-water area in recent 30 years. Based on the drilling results of Well BD21, geological conditions and enrichment law of hydrocarbon accumulation are systematically summarized in the northern fault terrace zone in Baodao Sag. Study results show that a large-scale source rock of Yacheng Formation is developed with high maturity and strong capacity of hydrocarbon generation. The fault activity was weak during the two stages of hydrocarbon charging, and the tectonic evolution matched well with the timing of hydrocarbon supply. The high-effi ciency hydrocarbon migration pathways are formed by the combination of reservoir and faults which connect with source rock in both vertical and short-distance lateral directions. The regional caprock covers the whole spatial range of hydrocarbon generation, migration and accumulation, providing good sealing capacity. The northern fault terrace zone is favorable exploration target in Baodao Sag, which shows great potential of large-scale structural-lithologic oil and gas reservoirs in deep-water slope zone.