The Upper Paleozoic coal-bearing formation in Bohai Bay Basin is the major source rock in the Paleozoic strata.It had experienced complicated history of bury

thermal maturation and hydrocarbon generation of multiple episodes.The petroleum system in the Upper Paleozoic of the areas features in late reservoiring and it is only meaningful when it happened in effective reservoiring period with later hydrocarbon generation.Three types of hydrocarbon generating history are classified by establishing the geologic model of hydrocarbon generation in the Upper Paleozoic.The areas such as Dongpu sag with a burial history of uplifting in Yanshanian period and deep burial in Yanshanian period are the most potential for secondary hydrocarbon generation

the areas such as Dongying sag with a burial history of shallow burial in Yanshanian period but deep burial in Himalayanian period have relatively large potential of secondary hydrocarbon generation

while the areas such as Shenxian sag expe-rienced relatively deep burial in Yanshanian period and relatively shallow burial in Yanshanian period have limi-ted potential of secondary hydrocarbon generation.Numerical simulation is carried out to evaluate the hydrocarbon generating intensity at different stages.It reveals that the quantity of hydrocarbons generated in Cenozoic accounts for 60% of the total in Jiyang depression

14% in Linqing depression

as high as 90% in Dongpu sag is.Simulation of hydrocarbon generation history indicates the plane distribution of hydrocarbon generating intensity in Jurassic-Cretaceous and Cenozoic

and the resource potential and exploration targets of the Upper Paleozoic natural gas in Bohai Bay Basin.