Abstract: Nanwu Sag of the South Yellow Sea Basin is one of the most favorable hydrocarbon accumulation areas in the Mesozoic-Cenozoic Basin in the South Yellow Sea, with good exploration potential. However, due to its complex structural characteristics, no breakthrough has been achieved in oil and gas exploration. Using the latest 3D seismic and drilling data, this paper analyzes the structural characteristics of Nanwu Sag on the basis of fine structural interpretation. It is concluded that Nanwu Sag has experienced two major stages of tectonic evolution, fault depression and depression, with two stages and three groups of normal faults. Under the control of faults, three local structural belts are developed, mainly composed of fault nose and fault block traps. The hydrocarbon accumulation in Nanwu Sag has the characteristics of near-source and near-fault accumulation, and the development of deep and large faults is the key factor for hydrocarbon transport. Through the study, the structural characteristics and key factors of accumulation in Nanwu Sag are summarized, and it is proposed that the northern slope belt has deep and large faults, and good trap conditions, which is a favorable exploration zone.The study has reference significance for the exploration work of Nanwu Sag.