[Objective] In order to provide the theoretical basis for evaluating the effect on soil microbial properties and for establishing reasonable sustainable forest management to reduce soil erosion and land degradation, soil chemical properties and microbial biomass of main tree species-Robinia pseudoacacia and Quercus varaibilis in rocky mountain area of northern China were studied. [Methods] The chemical properties, microorganism amount, microbial biomass carbon and nitrogen in soil of R. pseudoacacia and Q. varaibilis plantations were analyzed. The factors influencing soil fertility were also studied with principal component analysis and stepwise regression analysis. [Results] The results showed that three kinds of main soil microorganisms and microbial biomass carbon and nitrogen decreased with the deepening of the soil depth. The amount of soil bacteria in the R. pseudoacacia plantation was 2.13-2.26 times that in the soil of Q. varaibilis plantation. While the amount of actinomycetes in the soil of Q. variabilis plantation was 4.48-6.05 times that in the soil of R. pseudoacacia plantation. No obvious difference was observed between the amounts of fungi in these two kinds of forest soil. The content of nitrate nitrogen, organic matter, available phosphorus and the total amount of microbes, microbial biomass carbon and nitrogen in the soil humus layer of R. pseudoacacia plantation were significantly higher than that of Q. variabilis plantation. [Conclusion] (1) The soil physical and chemical properties and the number of microorganisms and microbial biomass carbon/nitrogen could be used to reflect the variability of soil fertility in this area. (2) The main factors affecting the total amount of microbes and microbial biomass carbon/nitrogen are total nitrogen, available phosphorus and available potassium. (3) Planting R. pseudoacacia is more conducive to the ecological restoration of soils than planting Q. varaibilis.