Abstract: Based on the investigation of the Holocene soil in the Guanzhong area and data of the appraisal of soil microstructure from optical microscope and electronic microscope and chemical analysis, the subdivision of soil profile, soil type developed in the Holocene Megathermal were studied in the paper.The investigation shows that Holocene soil profile generally consists of organic horizon (A), clay grouting horizon(Bts) and illuvial horizon of CaCO₃(Ck), but some of soil profiles consist of organic horizon, clay grouting horizon, weathering-leaching parent loess horizon(Cl) which only occurs in leaching soil and illuvial horizon of CaCO₃.The analysis of CaCO₃ shows that CaCO₃ content is low in clay grouting horizon and weathering-leaching parent loess horizon in the Holocene soil, and generally is less than 0.8%, which indicats a stronger leaching process during the formation of the soil.The content difference of Al₂O₃ and Fe₂O₃ from the upper to the lower of the Holocene soil profile is 1.0% and 0.7% respectively, indicating the formation of Al₂O₃ and Fe₂O₃ in soil formation process and a stronger chemical weathering process.There is reddish brown illuvial clay films, which is a characteristic of leaching soil, about from 5% to 10% in the middle of clay grouting horizon in the Holocene soil, and its content is more than luvic cinnamon soil and is close to weakly developing subtropical yellow-brown earth.Clay content in clay grouting horizon is from 38% to 58.6%, and in the weathering-leaching loess horizon is from 32.3% to 40.7%, which is higher than that in unweathering loess horizon and is a result produced by stronger clay grouting.The appraisal from electronic microscope shows that transparent clay film in the Holocene soil was mostly composed of secondary clay mineral micro-crystals, and the micro-crystals was ranged directionally, which is the reason why clay films posses optical character that like a crystal.By x-ray diffraction, it is known that mineral of mixed layer of illite and askanite is dominant in micro-crystals in clay films.Based on above data, the soil in the Middle Holocene was leaching soil, and soil formation action was stronger at that time than at present, soil type should be weakly developed subtropical yellow-brown earth, the climate was obviously warmer and wetter at that time than at present; in the Middle Holocene, air masses bearing water in summer coming from southeast sea can frequently reached the area,and the Qinling Mountains had lost the function as the boundary between temperate zone and subtropical zone, and two sides of the Qinling Mountains both were subtropical climate.