The soil nutrient, microorganism and enzyme activity are studied and analyzed in Pinus sylvestris var.mongolica plantations in Zhanggutai area. The results are as follows:the differences of microorganism quantity among different type of soil is the significant, so are the enzyme activity and soil nutrient. The correlation among soil microorganism quantity, enzyme activity and soil nutrient content is the significant,it can be used as evaluation index of soil fertility. The strategy and measures to prevent the soil degradation of Pinus sylvestris var.mongolica were put forward,including application of thinning rationally for existing dense plantations and establishment of mixture forest for new plantations.