This study investigated four typical artificial vegetation types (Pinus sylvestris, Pinus tabulaeformis, Populus L., and Caragana korshinskii) and grassland in the agro-pastoral transitional zone in order to explore the characteristics of soil carbon (C), nitrogen (N), phosphorus (P) and their stoichiometric ratios within the 0-100 cm soil layer. The results showed that: 1) Topsoil (0-20 cm) organic carbon (SOC) contents of grassland, Caragana korshinskii, Populus L., Pinus sylvestris, Pinus tabulaeformis were 7.72, 7.16, 4.16, 15.59 and 15.84 g/kg, respectively; Total nitrogen (TN) contents were 1.12, 0.58, 1.27, 1.23 and 0.87 g/kg, respectively; Total phosphorus (TP) contents were 0.24, 0.20, 0.31, 0.14 and 0.25 g/kg, respectively. All were lower than those of the national average levels, indicating the lower soil fertility. 2) SOC was in an order of Pinus tabulaeformis>Pinus sylvestris> Caragana korshinskii >grassland>Populus L., TN and TP in the poplar forest were highest among different soil depths. TN of Pinus tabulaeformis in the 0-20 cm layer was higher than that under grassland. TN in the 50-100 cm layer under Pinus sylvestris was higher than that under the grassland, while TN under Caragana korshinskii was lowest and lower than that under the grassland. Except for the Populus L. forest, TP under other artificial vegetation were lower than that under the grassland, with Pinus tabulaeformis being the lowest. In each soil layer, C︰N and C︰P ratios under different artificial vegetation were higher than those under the grassland, generally in an order of Pinus tabulaeformis> Pinus sylvestris > Caragana korshinskii > Populus L., > grassland. In the 0-20 cm layer, only N︰P ratio of Populus L., exceeded that under the grassland, while in the 20-100 cm layer, N︰P ratios of all vegetation was higher than that under grassland. 3) The correlation between soil C and N, P was not significant, while N and P showed a significant positive correlation. SOC had the hight correlation coefficient with C︰N and C︰P, indicating SOC was the primary regulator of C︰N and C︰P ratios, while N︰P was only significantly correlated with TN, suggesting that N︰P was mainly regulated by TN.