Abstract: An  investigation was conducted to study the relationships of soil organic carbon (SOC) content with root biomass and soil moisture content as well as the accumulation mechanisms of SOC under the Elacagnus angustifolia-Achnatherum splenden community in Ningxia Hui Autonomous Region of Northwest China. The results showed that the SOC content decreased gradually with increasing soil depth, and changed gently in both horizontal and vertical directions. The correlations of the SOC content and its affecting factors varied with soil depth. In 0-30 cm layer, the SOC content was significantly negatively correlated with soil moisture content; in 60-150 cm layer, the SOC content was significantly positively correlated with soil moisture content and root biomass. Partial regression analysis indicated that the root biomass density in 0-30 cm soil layer contributed significantly to the variance of SOC content. In 60-150 cm layer, the SOC content was mainly affected by root system and soil moisture content; in 30-60 cm layer, no significant correlations were observed between the SOC content and the root biomass and soil moisture content. There was an obvious difference in the accumulation mechanism of SOC in different soil layers and at different locations of E. angustifolia-A. splendens community.