As every tree species is unique in biological and ecological characteristics, the presence of mono-species stands of forests, natural or planted may cause variation of soil properties away from equilibrium toward imbalance or certain extremity, which is called “soil polarization” by the author. At the same time, a number of characterization indexes, i.e. width of anti-polarization (W), resistance to polarization (R), polarization (P) and ratio of polarization resistance to polarization (I = P/R) were proposed for polarization analysis based on results of determination of soil properties of soil samples collected from a variety of mature stands of pure and mixed forests using a multi-point mixed sampling method at multiple sites in the semiarid, hilly area of loess plateau. Results show very strong polarization (P>0.20) of the following soil properties: chemical properties under Pinus tabulaeformis forest; chemical and biological properties under Platycladus orientalis, Robinia pseudoacacia and Hippophae rhamnoides forests; chemical, biological properties and trace elements content underUlmus pumila forest; biological properties under Betula platyphylla forest; and biological and physical properties under Acer ginnala forest. Among the species in this study, pure stands of P. tabulaeformis and R. pseudoacia resulted in serious depletion of soil nutrient reserves; Pure stands of P. orientalis increased soil fertility; Pure stands of U. pumila increased soil fertility but decreased trace elements content; Pure stands of B. platyphylla worsened soil biological properties; Pure stands of A. ginnala led to depletion of soil nutrient reserves and deterioration of soil biological properties; and Pure stands of H. rhamnoides did to depletion of soil nutrient reserves and degradation of soil biological and physical properties. The anti-polarization capacities of P. simonii and P. tabulaeformiswere the highest and of U. pumila the lowest. Relative to antipolarization capacity, the ratios of polarization resistance to polarization of the stands fell into the category of more than “medium” （I_a＞0.40）including chemical and physical properties under P. tabulaeformis forest, all the soil properties as a whole under P. orientalis, R.pseudoacia and U. pumila forests, and biological, physical and chemical properties under B. platyphylla forest.