[Objective] The response characteristics of carbon and nitrogen in rhizosphere soil of semiarid grasslands and soil microbial biomass to different years of grazing exclusion were studied to provide basic information for the study of the material cycle of semi-arid grassland ecosystems and the determination of ecosystem nutrient limits, and to determine reasonable grazing exclusion periods.[Methods] Taking the typical semi-arid grassland of Yunwushan National Nature Reserve in Guyuan City, Ningxia Hui Autonomous Region, as the research object, the ecological stoichiometric method was used to compare and analyze the variation process and rule of rhizosphere soil organic carbon, total nitrogen, nitrate nitrogen, ammonium nitrogen, and soil microbial biomass carbon and nitrogen content, as well as the stoichiometric characteristics of the grazing land and the sampled land enclosed for 10, 25, and 35 years.[Results] Enclosure treatment significantly increased the soil carbon and nitrogen content. The maximum values appeared in the plot enclosed for 25 years, after which the values declined. The soil organic carbon contents of the plots enclosed for 10, 25, and 35 years were 1.37, 1.83 times and 1.38 times of that of the grazing plot, and the total nitrogen contents were 1.34, 1.52, and 1.24 times of that of the grazing land, respectively. However, soil C:N remained stable with the increase in enclosure years. It was significantly correlated with soil organic carbon content but had no evident correlation with soil total nitrogen. Compared with that of the grazing plot, the ammonium nitrogen content of enclosed plots did not change significantly with the enclosure years, but the nitrate nitrogen content and the nitrate:ammonium nitrogen ratio generally decreased, with the lowest values at 25-year grazing exclusion. Enclosure significantly increased the soil microbial biomass carbon and nitrogen content. The soil microbial biomass carbon contents of the sample plots enclosed for 10, 25, and 35-years increased by 20.5%, 45.7%, and 15.1% compared with grazing land, while the microbial biomass nitrogen contents increased 24.7%, 60.5%, and 40.9%, respectively. The microbial biomass C:N value decreased with the extension of the enclosure period. The percentage of microbial biomass carbon in soil organic carbon did not respond to the enclosure period. Compared with grazing land, 10-year and 25-year grazing exclusion had no significant difference in the percentage of microbial biomass nitrogen in total soil nitrogen and the stoichiometric imbalance (i.e., the ratio of soil C:N to microbial biomass C:N), but the value significantly increased in 35-year grazing exclusion.[Conclusion] Enclosure measures can significantly improve soil carbon and nitrogen nutrients in semi-arid degraded grasslands, promote soil microbial activities, and facilitate the restoration of degraded grassland. However, a too long enclosure treatment may have a negative effect. Twenty-five years of enclosure is a reasonable enclosure period in long-term enclosure measures of degraded grasslands.