The article analyzes the sedimentary systems and hydrocarbon accumulation in the Palaeogene Chengbei Sag in the Bohai Bay Basin. The researchers studied the sedimentary evolution, facies types, and reservoir characteristics of the area. They found that the Chengbei Sag went through four stages of development and has five main sedimentary facies. The Palaeogene reservoir can be categorized into two accumulation systems and three types of reservoirs. The study shows that sedimentary characteristics play a significant role in hydrocarbon accumulation, with easier accumulation in certain areas like updip pinchout sandstone and overlap unconformity regions.