Abstract: Baibei sag is a secondary tectonic unit of Chuanjing depression in the west margin of Erlian basin,and the prospecting degree is low and the exploration effect is not ideal.Through comprehensive analysis of the oil source,reservoir,cap rock,and trap accumulation conditions,the results show that each layer is developed lacustrine mudstone of lower cretaceous hydrocarbon source rock,with good hydrocarbon source rock organic matter content and good organic matter types,but the maturity is generally low,considering the factors of hydrocarbon source rock maturity,effective hydrocarbon source rock distribution is only developed in A'ershan group.On the plane,it is distributed in the center of the east and west two sub-sags.Lower cretaceous reservoir is mainly of fan delta,alluvial fan,subaqueous fan and deep lacustrine turbidite fan sand body development.Cap rock condition overall is good,near the center of the hollow tank,it is superior.Trap is more developed,mainly of the structural trap,lithologic trap,stratigraphic trap and complex trap.Oil and gas shows A'ershan good group is the main target layer in Baibei sag.The hydrocarbon accumulation pattern and superimposed accumulation elements have been established.A good set of favorable exploration zone has beenpredicted,favorable zones are mainly distributed in the northern steep slope belt in the east,and west of hollow tank,with superimposed area of 13.05 km2.