Abstract: According to the structural characteristics of brink sags in the Bohai Bay Basin,the formation and evolvement of the basin show the characteristics of passive rift basins,which are provided with inheritance,multi-direction extension and rotation strike-slip.In co-ordination with the structural characteristics of host sags,the rift-subsidence which occurred in Cenozoic in the background of area stress actions and fault-block movements in the Bohai Bay Basin is summarized in this paper.Together with the northward extension caused by the unbalance of fault blocks moving northward,the northern plate extended north-westward inner due to the difference of movement between speed and distance from the east to the west of the plate.During the differential movement of fault-blocks tilting and extending process,the Tan-Lu fault belt adjusted in the strike-slip process and made shearing stress release effectively.At the same time,a series of strike-slip sags were formed along the fault belt.The formation model of the Bohai Bay Basin can be summed up as:the crust extension-the crust rift and extension as well as the sub-geosphere viscoelasticity rheid becoming thinner-the mantle uplift-the mantle plume invasion and melting-(the crust rise and erosion)-the thermal subsidence.