Yangjiawan section (34°03’41″N, 109°32’51″E), 50 km to the east of Xi’an, lies in the south central area of Guanzhong Plain. Forty-one samples were collected from the section of S1 paleosol at a interval of 5 cm. The major oxides and trace elements are analyzed by X-ray fluorescence analysis. The migration depth of Fe2O3 and CaCO3, the layer and thickness of weathering and leaching loess has been observed in the field. It is observed that the deep weathering and leaching loess has developed under the S1 paleosol, more than 2 m than nowadays. The apparent migration of red ferruginous clay film indicates that the soil has undergone acidic weathering stage. The distributive characteristics of Fe2O3, CaCO3 and the development of deep weathering and leaching loess indicate that the S1 paleosol was subtropical yellow brown forest soil, belonging to acidic alfisol.