Abstract: In order to correctly understand the features of extremely heterogeneous hydrocarbon distribution and rich in the east and poor in the west and the controlling factors in Weibei sag of the Bohai Bay basin, this paper analyzes the hydrocarbon migration process and accumulation pattern on the basis of source rock and accumulation period analysis and oil?source rock correlation. The result shows that the oil and gas mainly accumulate in the Eocence Kongdian formation in this sag, and there are significant differences on hydrocarbon accumulation and main controlling factors in the east and in the west: the oil and gas in the east mainly came from the sources rocks of the middle and upper sub?member of Ek developed in nearly eastern part of the northern sub?sag belt, and accumulated during Es4 to Ed depositional period. Tectonic movements resulted in the steplike, uplifting migration of hydrocarbons from the north to the south. Microstructural ridges acted as the predominant pathways for oil and gas migration with a migration and accumulation mode of“bidirection conduction?lateral migration”. The key to good hydrocarbon accumulation is moderate structural movement during entrapment and good preservation; the oil and gas in the west mainly came from the sources rocks of the middle and lower sub?member of Ek in this sub?sag which suffered from 2 times of hydrocarbon generation during Es4 to Ed depositional period and late depositional period of Minghuazhen formation, respectively. Its accumulation is featured with the“entrapped during 2 different periods?the accumulated near source rocks”, large burial depth and tight reservoir. Deep?burial near?source gas reservoirs around the secondary hydrocarbon?generation center are the targets for oil and gas exploration in the western areas