By taking key factors controlling hydrocarbon accumulation of lithologic reservoirs, it is concluded that the geological conditions in the Gaoyou sag are favorable for forming lithologic reservoirs. Since the time oil entrapment is at the strong filling dynamic window, the physical property of reservoirs is more profitable than that of filling critical physical property and the lithologic traps is early developed. The lithologic reservoir accumulation was controlled by two key factors: migration pathways and trap condition in the Gaoyou sag. It is required that the main fault opened early and closed later for oil accumulation in this study.