The Beidong sub depression in the Beier sag of the Hailar Basin is a late stage reformed fault depression, The fan bodies of the Nantun Formation in this area are characterized by multiple sources and multi-period development, primarily consisting of nearshore submarine fans, fan deltas, and lacustrine deposits. Accurate identification of fan body reservoirs is of significant importance for guiding subsequent exploration and development. Based on drilling, logging, and 3D seismic data, this study first utilizes triangular cycle filtering time–frequency analysis technology to divide the depositional periods of sandstone and conglomerate fan bodies. Then, guided by the principle of “source-to-sink” system which control sand in the faulted lake basin, the study applies eroded residual basement to identify the source areas, paleogeomorphology to analyze transportation channels, and 3D seismic analysis techniques such as model forward modeling, attribute clustering, and three-dimensional carving to analyze the convergence areas of the fan bodies, thereby delineating the boundaries and development scale of each period’s fan bodies in detail. The results indicate that the southern depression of the Beier area has developed five periods of fan bodies, with different distribution characteristics and scales for different periods. There is one main oil layer in the Nantun Formation, which is the third period of sandstone and conglomerate fan bodies. The research results have laid an important foundation for the exploration of oil reservoirs in areas with low exploration degrees.