A new concept of soil polarization was presented and defined as the non equilibrium or polarizing tendency of soil development that deviated from its original status of equilibrium due to long-term or continuous growth of the same single specie of trees,which was thought to be the fundamental obstacle to continuous growing of planted pure forest Based on this principle,both single and comprehensive index models were established,and criteria for gradation and a system for classification of soil polarization were also planned out In addition,these models were applied to a case study of planted pure forest of black locust (Robinia pseudoacacia L) in a gullied area,south in the Loess Plateau Results show that the soil therein falls in the po larization category of aridification plus sterilization.