Abstract: Since the property of clastic rock in the middle-deep strata in Bohai sea is poor,the lacustrine bio-carbonatite reservoirs with good property become the important oil and gas exploration target at present.Shahejie formation in Bohai X oilfield exactly belongs to this type of reservoir.Based on tectonic evolution background,through sedimentary facies and evolution analysis,it is considered that the bioclastic dolostone layer in this kind of reservoir experienced four stages,which can be identified as the early,the middle,the late stage of S1 lower sub-member,and the early stage of S1 upper sub-member.Combined with drilling data analysis,it is believed the development of the bioclastic dolostone layer is controlled by ancient landform,the layer usually distributed in the slope zone,the superposition thickness of multi period biodetritus beach was large,presenting lenticular distribution on the section.By establishing the theoretical model,combining with the drilling data,the scope and thickness for the reservoir development are predicted,which is of guiding significance for oilfield development of this kind.