【Objective】The knowledge about vegetation succession, is essential to vegetation restoration, especially in steppe regions on the Loess Plateau. Recently stoichiometry has been effectively used to illustrate plant community succession and vegetation restoration. Balance of carbon (C), nitrogen (N), and phosphorus (P) in plant has been a hotspot of the research on biogeochemical cycle and plant ecology. However, most of the studies have focused on nutrients in plant leaves, and few did on the elements in plant roots, let alone, on ecological stoichiometrical characteristics of the soils and plant roots in steppe regions under enclosure on the Loess Plateau, relative to enclosure history. 【Method】This paper explored ecological stoichiometrical characteristics of the soils and plant roots in grasslands different in enclosure history (1 a, 12 a, 20 a and 30 a) on the Yunwu mountain of Ningxia Province. The steppe region under study is located between 106°26′E and 106°30′E and between 35°59′N and 36°02′N. The Yunwu Mountain lies across the center of the Loess Plateau, with an altitude ranging from 1 000 to 1 800 m above sea level. The study area has a semi-arid climate, characterized by heavy seasonal rainfalls causing recurrent flooding and drought, with mean annual temperature being 5 °C and mean annual precipitation being 445 m. The typical natural vegetation of this region is grassland. Samples of the soils and plant roots in the region were collected and analyzed for organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP), and their stoichiometrical ratio and interrelationships, using the time-space substitution method, based on the principles of stoichiometry. 【Result】Result show that with the enclosure going on, soil bulk density decreased gradually, SOC and TN varied more significantly, while TP did less. In the early years of enclosure, SOC and TN declined first and then rose till the enclosure reached 20 or 30 years old, when they leveled off. Soil organic carbon, total nitrogen and total phosphorus varied in the range of 12.88~22.37, 1.41~2.48 and 0.66~0.74 in the 0~20 cm soil layer and in the range of 9.58~18.45, 1.09~2.12 and 0.58~0.70 in the 20~40 cm soil layer, respectively. Soil C:N, C:P and N:P ratio varied in the range of 9.04~9.63, 19.62~32.27 and 2.14~3.37, respectively, in the 0~20 cm soil layer and in the range of 8.68~9.22,15.74~26.32 and 1.80~3.03, respectively, in the 20~40 cm soil layer. Soil organic carbon, total nitrogen and total phosphorus were significantly correlated with each other. C, N and P concentration in the roots varied in the range of 357.6 to 381.4 g kg^-1, 7.35 to 8.18 g kg^-1 and 0.54 to 0.70 g kg^-1, respectively. In the root, C concentrations increased gradually with enclosure going on, whereas N and P concentrations were lower than the world’s average. C:N, C:P and N:P ratio in the root varied in the range of 44.52~59.02, 574.7~793.9 and 10.87~15.14, respectively, during the period of enclosure, showing that C:N varied more drastically, while C:P and N:P did less. Ecological stoichiometric characteristics of C: N: P in plant roots were more affected by soil than by the root per se. Soil TP affected the ecological stoichiometrical characteristics of carbon, nitrogen, and phosphorus in plant roots (p<0.01) more significantly than soil TN did (p<0.05). Besides, the vegetation in this region tended to be restrained by soil N concentration after the grassland was enclosed. 【Conclusion】The study on effects of enclosure on C, N and P in the soil and plant root of the grassland, their ecological stoichiometric characteristics and interrelationships may provide some scientific bases for the study on material recycling in the grassland ecosystem and nutrient restraints in the vegetation ecosystem, and some scientific references for accurate evaluation of ecological benefits of the policies or strategies of “Grain for Green” and “Enclosure of grassland”.