Root decomposition is an important underground ecological process of carbon and nutrient cycling in terrestrial ecosystems. Studying the root decomposition characteristics of typical plants and their effects on soil nutrients in the mountainous area of southern Ningxia can provide a basis for nutrient cycling between plants and soil in vegetation restoration in Loess Plateau of China. The decomposition characteristics of three typical plant roots and the trend for soil nutrient change in the South Ningxia Loess Hilly Region of Northwest China, were studied for 2 years using the buried bag method. The results showed that the annual decomposition indices (K) of Stipa bungeana, Artemisia sacrorum, and Thymus mongolicus roots were 0.00891, 0.01128, and 0.01408, respectively, and the decomposition rate in turn showed as Thymus mongolicus > Artemisia sacrorum > Stipa bungeana. After 16 months, a substantial amount of root nutrients had been released. The release amount of carbon was 57.05-124.39 g/kg while for nitrogen it was 0.12-0.47 g/kg. The effects of three typical plant roots on soil nutrients were as follows: the contents of soil organic carbon increased by 0.17-0.35 g/kg in a 0-5 cm soil layer, and by 0.26-0.35 g/kg in a 5-20 cm soil layer. Correlation analysis showed that some negative correlation exists between the release amount of root nutrients and soil nutrient content. When the soil nutrient content is low, roots will increase nutrient release to supplement soil nutrients. This indicates that root decomposition increases soil nutrient content and effectively promotes nutrient cycling in the root-soil system.