As the first sediment in Cenozoic time in Ningxia region, the Eocene Sikouzi Formation has special tectonic meaning, however, its development has not been interpreted satisfactorily yet. From the point of deposition scope and more radical change of sedimentary facies, the Sikouzi Formation occurred abruptly. By the means of facies and structural analysis, the authors think that the Sikouzi Formation was deposited on the forebulge facing to the Corridor Nan Shan which resulted in the development of one foreland basin 30-40 Ma ago, the forebulge unit of this foreland basin was located along the western margin of Ordos Basin and Xiangshan area, the back-bulge unit lay to the east of western margin of Ordos Basin. Because of flexing, many normal faults dipping to the orogen came into being on the forebulge, it was these normal faults that controlled the distribution of Sikouzi Formation which was deposited rapidly and formed a serial of alluvial fans around forebulge, the provenance of it was the uplifts along the western margin of Ordos Basin and Xiangshan area, etc.