In order to clarify the effects of different ages of Robinia pseudoacacia forest on soil nutrient and ecological stoichiometric characteristics, we selected four kinds of artificial Robinia pseudoacacia forests of different ages (10 years, 15 years, 25 years and 40 years) located in Yan’an, Shaanxi province to investigate the distribution patterns of soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP) and total potassium (TK) in 0—200 cm soil layer, and analyzed the ecological stoichiometric characteristics. Three sample sites were set up in each selected Robinia pseudoacacia forest and three sampling points were set randomly. Soil samples were collected to analyze soil C, N, P, K and stoichiometry. The results showed that: (1) SOC，soil TN and TK increased with the growth of Robinia pseudoacacia forest on the whole, and the change of soil TP with the growth of Robinia pseudoacacia was not obvious. There were significant positive correlations among SOC, soil TN and TP. (2) The spatial distribution of SOC and soil TN were quite consistent, showing the same trend of declining first then tending to be relatively stable with soil depth, and they were higher in the surface layers than in the subsurface layers. TP was lower than SOC and TN in spatial variability．The content of TK was higher than that of SOC, TN and TP, and it did not change much with soil depth. The 15 years occurred the minimum value. (3) Soil C∶N ratio, C∶P ratio, N∶P ratio, C∶N∶P ration all decreased first and then deceased with the growth of Robinia pseudoacacia forest. (4) Soil C∶N didn’t change much, as soil C∶P, N∶P showed the same trend with SOC and TN with soil depth.