In order to study the effects of different plantation densities on the soil physicochemical properties of Betula platyphylla natural forests, this study analysed the patterns of changes in soil physicochemical properties under varying stand densities, and provided reasonable density references for the protection of Betula platyphylla natural forests. The Betula platyphylla natural secondary forests in Baoku Forest Area, Datong County, Xining City, Qinghai Province were used as the research object, soil surface and deep layer samples were collected to investigate and determine the soil bulk density, soil water content, field capacity, total porosity, capillary porosity, non-capillary porosity, saturated hydraulic conductivity (K_st), soil pH value, soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), alkali-hydrolyzed nitrogen (AN), available phosphorus (AP), available potassium (AK) content, and a total of 17 soil property indicators including C ∶ N, C ∶ P, N ∶ P. Soil attributes were investigated for six different stand densities of 100-400、400-700、700-1000、1000-1500、1500-2100、2100-2500 plant·hm^-2. The data were tested for significance and correlation analyzed using SPSS22.0. The Least Significant Difference (LSD) method and Duncan's Analysis (Duncan) in One-way ANOVA were applied to test the differences in soil physical and chemical properties across different densities and soil layers. The results showed that: (1) In terms of vertical distribution characteristics, soil porosity, K_st, the contents of soil SOC, TN, TP, AN, AK and the ratios of C ∶ P and N ∶ P showed a decreasing trend with the increase of soil depth. Conversely, soil bulk density and soil pH value increased with the increase of soil depth. (2) In terms of density distribution characteristics, the contents of soil SOC, TN and AN, as well as the ratios of C ∶ P and N ∶ P, showed a slow decreasing trend as density increased, and TP content shows no significant change with increasing density, all of the these indicators reached its maximum values when the density was 100-400 plant/hm². The soil water content, field capacity, K_st, and porosity first increased and then decreased with increasing density, and these indicators reached their maximum at a density of 400-700 plant/hm², while the soil bulk density reached its minimum at this density. (3) In terms of soil stoichiometric characteristics, the average values of soil C ∶ P and N ∶ P in the study area are 97.32 and 7.36, which are higher than the average values of Chinese soils, indicating that soil P effectiveness was low. In summary, when the density of birch forests in the study area is low (100-700 plant/hm²), the improvement effect of soil physical and chemical properties is relatively good, which will be more conducive to the stability of soil physical structure and nutrient accumulation.