Based on the cosine transform method and using the method of upward continuation and computed base depth of the basin using the inverse technique, the authors had processed the Hulin Basin Bouguer gravity anomalies and inversed the base depth. Then the authors studied differences of underlying structure between south and north of the basin reflected by geology and geophysics. It is shown that the south fracture of Dunmi fault, which was composed of two faults, is vertical and strike-slip fault, it controls strike-slip movement of its bilateral fault block and the formation and evolution of the basin. If let Dunmi south fault as dividing line, the Hulin Basin can be divided into two basins, i.e. south basin and north basin, and their geology and geophysics properties are totally different. The north basin is part of large Sanjiang Basin, whereas the south basin is an independent basin system.