Abstract: According to the present system of soil classification in China, forest soils in the low mountain areas in northeastern Jiangxi province should be allocated to the soil great groups of red earths and yellow earths. Nevertheless, those soils of yellowish brown color situated above the waist of a mountain slope do not conform to the concept of red earths or yellow earths mentioned above in reality. In this paper a figure of minimum spanning tree, containing data on several soil profiles within the low mountain areas in northeastern Jiangxi province and the low mountain areas in the suburbs of Nanjing City, Jiangsu province (northeast of the former) and based upon the 5 properties of subsoil diagnostic for the higher categories of soil classification, illustrates that the soils of red color on the lower part in a slope of the low mountain areas in northeastern Jiangxi province are completely different from those of yellowish brown color at the places above the middle, thus the two types of soils should belong to two different soil great groups respectively. The latter is close to the soil profiles with a buried red layer on the lower part of a low mountain slope near Nanjing, but the causes of formation of the two soils are not the same. The patterns of soil association of the two researched areas have been affected by the ancient climate. The soil association in the low mountain area near Nanjing includes the Rankers (similar to the Shantung burozems in properties) in the upper and the Yellow-brown Earths (derived from fossil red earths) in the lower while the soils in the low mountain areas of northeastern Jiangxi province includes the Yellow-brown Earths (soils of yellowish brown color formed in modern time) in the upper and the Red Earths (derived from the anciently weathered crust) in the lower.