The Gabon basin is a sedimentary basin with oil and gas in the passive continental margin of West Africa, and is considered as a main hydrocarbon exploration area. The G block is a key investment block in north Gabon sub-basin. The petroleum geological conditions of the G block are favorable. As a typical oil and gas reservoir in the passive continental margin basin, the oilfield in the G block could be a good reference for other blocks in terms of the geological condition and the hydrocarbon accumulation and distribution. In order to reveal the hydrocarbon accumulation and its main control factors for the oilfields in the G block, this paper analyzes the source rock, the reservoir, the cap rock, the trap and the hydrocarbon migration system in terms of stratigraphic and structural characteristics. It is confirmed that in the G block there are high quality resource rocks, sand reservoirs of good petrophysical properties, and the reservoir and seal assemblage is good. The U.P.C. member is the main pay zone in the G block. The oil reservoirs in the G block are mainly structural traps such as the anticline and fault blocks controlled by tectonic activities, and the hydrocarbon accumulates mainly in the high structural closer. This paper presents the accumulation model in the G block, including the generation and feed from the deeper source rock, the migration through faults, salt and sandstone, the oil and gas accumulation in structural traps, and the main factors for the hydrocarbon accumulation are traps related with salt structure.