Abstract: Through systematic analysis on development characteristics of sublacustrine fans in Bohai oilfield,the sublacustrine fans of Bohai oilfield could be divided into two depositional models:one type was related to early inherited slope break belt and the other was related to synsedimentary slopebreak belt built by large delta construction.The sand-rich characteristics and the scale of these two types was compared and analyzed.By taking BZ21 area as an example,based on the analysis of palaeomorphologic patterns and synsedimentary slope break belt,by means of fine seismic tracing and composite microfacies features description,the depositional models of large-scale sublacustrine fan group in BZ21 area were established,which found sand-rich areas,described sadrich boundaries and pointed out favorable subtle reservoir exploration targets of sublacustrine fan types in BZ21 and BZ19 areas.