Mid-subtropic is a major part of the subtropical zone in China,which occupies about 17.6 percent of the country’s total area.The climate is warm and humid there,with high precipitation and high temperature appearing at the same period.Areal differentiation of topography,natural resources,vegetation and soil is obvious,particularly in the eastern and western part.So it is necessary to delineate a objectively scientific basis for natural regionalization,and for rational allocation of agriculture,forestry and animal husbandry. The differences between eastern and western parts of the mid-subtropical zone obviously lie on the various composition of natural environment and the way of land use. Much controversy has been evoked about to where the demarcation line should be drawn within Hunan province and what are the criteria based on.After careful study on the differentiation in local terrain,hydro-thermal conditions as well as field survey in Hunan province,the authers would like to assign the demarcation line betwen the west and the east of mid-subtropics in Hunan province existing on the northeast of Wu-Ling Mountain,across Yuan river to east flank of Xuefen Mountain.From north to south the demarcation line passes through several counties:Shimen,Linfeng,Taoyuan,Huangcai (Ningxiang), Dongkou,Wugang,Xinning up to the administralive boundary line between Hunan and Gungxi provinces.