To investigate the evolution of planting years on soil carbon, nitrogen, phosphorus densities, and eco-chemical stoichiometry in Halaxylon ammodendron plantations, an age sequence of H. ammodendron stands (3, 6, 11 and 16 years) were selected in desert area of Jilantai, densities and stoichiometry characteristics of soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP) at soil depths of 0-20, 20-40, 40-60 cm were measured. The results showed that:(1) The contents and densities of SOC and TN in 0-60 cm soil increased with the increase of stand age, whereas the content and density of TP decreased with the increase of stand age. The SOC and TN contents and densities increased with the increase of soil depth in 3-year and 6-year plantations, and the content and density of TP were moving in exactly the opposite direction. The contents and densities of SOC, TN and TP increased with the increase of soil depth in 11-year and 16-year plantations. (2) The C:N, C:P and N:P ratios were 2.24~9.21, 1.59~7.05 and 0.56~0.81 with moderate spatial variation, and the coefficient of variation decreased with the stand age and soil depth, indicating that soil C:N, C:P and N:P ratios tended to remain stable. (3) Stand age, soil depth, and their interaction had a significant effect on SOC content, SOC density, C:N and C:P ratios, but had no significant effect on the N:P ratio and the contents and densities of TN and TP. (4) Soil porosity (STP) had a significant positive correlation with SOC density (P<0.05), indicating that the increase of soil porosity is helpful to increase SOC density and improve soil fertility. Plantation of H. ammodendron can improve soil fertility and soil environment in arid desert area.