Abstract: In order to evaluate site quality for afforestation in the arid region of loess covered by low woodland and shrubs mainly consisting of Caragana korshinskii Kom.a quantitative method was employed.Based on the quantification of critically ecological factors as independent variables,which affect the growth of trees,a deterministic mathematical modle was established to predict fresh weight of C.korshinskii at the age of four years through multiple regression analysis.Thus the fresh weight above ground can be used as criterion to evaluate the site quality before starting afforestation.