Abstract: This paper presents numerical simulation of the Cenozoic paleo?tectonic stress field in Qingdong sag of southeastern Bohai Bay basin using 2?D finite element method, analyzes the differences and space distribution regularity of the Cenozoic tectonic stress fields in different stages and discusses the relationship between the tectonic stress field characteristics and the hydrocarbon migration and accumulation. The results show that the sedimentary period of the Kongdian group and the lower part of the fourthmember of the Shahejie formation is the structural transformation period, in which Qingdong sag is located in NNE-SSW tension stress field, dominated by NW fault system, Tanlu fault left?lateral strike?slip process is weaker than the tension; during the sedimentary period of its second member to the upper part of the fourth member of the Shahejie formation, Qingdong sag is in NNW-SSE tension stress field, Tanlu fault becomes right?lateral strikeslip process, the strike?slip and tension processes are all stronger; during the sedimentary period of the frist member to Dongying formation, Qingdong sag is in right?lateral shear stress field, the basin regional tension stress field becomes weaker; by the end of sedimentary period of Dongying formation, Qingdong sag is in right?lateral compressive tectonic stress field, Tanlu fault is transformed from dextral tenso?shear period into dextral compresso?shear movement; during the sedimentary period of Guantao formation to Minghuazhen formation,Tanlu fault has weak dextral shear process and tension stress. In key period of hydrocarbon accumulation of Qingdong sag, the hydrocarbons in its favorable hydrocarbon?generating zone migrate along NW-SE direction under the process of NS and NNW-SSE maximum principal stress into the slope zone and transition zone in the west and the strike?slip belt in the east, respectively. So the low?value area of minimum principal stress and the high?value area of shear stress in this basin now could be the favorable zones for hydrocarbon migration and accumulation