Abstract: Hydrocarbon source rocks in the Northern Sag of Miaoxi of the Bohai Sea are studied based on the latest 3D seismic, drilling, logging, hydrocarbon source rocks and oil testing data for revealing their geochemical parameters, distribution patterns and forming environment. Basin simulation and mixed oil contribution analysis technique have been adopted for evaluation of main hydrocarbon source rocks and their exploration potentials. Results show that there are two sets of source rocks in the Northern Sag of Miaoxi, called Ed and Es12 respectively. The source rock Es12, which contains high abundance of matured organic matter of good type, is the major source rock in the Sag, of which the amount of hydrocarbon expulsion accounts for 56% of the total. Oil-source correlation further suggests that the crude oil of PL15-2 oilfield is mainly derived from the source rocks Es12. More data indicate that the Northern Sag of Miaoxi has a great exploration potential of hydrocarbons.