In order to clarify the stoichiometric characteristics of soil nutrients during vegetation restoration in alpine sandy areas. This study utilized the Populus cathayana plantation with varying restoration years (5, 10, 15, 20, and 25 years) in the sandy area at the northeastern edge of the Qinghai-Tibetan Plateau as the research subject, to investigate the contents of soil organic carbon (SOC), total nitrogen (TN) and total phosphorus (TP) in the soil depths ranging from 0 to 200 cm, along with their stoichiometric characteristics and interrelationships. The results indicated that SOC and TN contents increased significantly with the restoration years, with average SOC and TN contents in the 10—25 restoration years increasing by 11.0%—65.9% and 11.4%—37.4%, respectively. Compared with that in 5 years of restoration, however, TP exhibited a trend of initial increase followed by decrease. The changes in SOC, TN and TP contents in different soil depths were relatively stable under the same years of restoration. Soil C:N ratio exhibited an increasing trend over the restoration years, while the C:P and N:P ratios initially decreased before subsequently increasing. Additionally, C:P and N:P ratios were greater in the surface layer of 0—30 cm than in the deeper layer of 50—200 cm. Highly significant positive correlations (P<0.01) were found between soil SOC and TN contents. Additionally, stoichiometric ratios of C:P exhibited strong positive correlations with both C:N and N:P (P<0.01). Moreover, the N:P and C:P ratios were significantly associated with the concentrations of SOC, TN, and TP. SOC, TN, TP and their stoichiometric ratios were significantly influenced by the restoration years, with the effects exceeding those of soil depth and their interaction. Principal component analysis revealed that soil stoichiometric characteristics were influenced by distinct factors in the early and late stages of vegetation restoration. Soil stoichiometric characteristics in the early stage of vegetation restoration were influenced by soil properties and, in the late stage of restoration, by the interaction between root characteristics and soil stoichiometric characteristics. In conclusion, the establishment of P. cathayana plantation forests enhanced soil nutrient content, with the restoration years being the primary influencing factor. The accumulation rate of soil SOC was greater than that of soil TN, thus it is recommended to increase nitrogen fertilizer application or to introduce nitrogen-fixing plants in future vegetation restoration efforts. The characteristics of soil C, N and P contents and their ecological stoichiometric ratios in alpine sandy areas varied according to the restoration years and the soil depth. Therefore, these variations should be considered when constructing soil biogeochemical models.