Irrigation and cultivation are two important driving forces of variation of soil organic carbon density (SOCD). The Ningxia Irrigation Zone using water diverted from the Yellow River in irrigation was selected as a case for study, and 48 sampling points were set up in five types of soils to study characteristics of soil organic carbon (SOC) and SOCD in these soils under different cultivation and irrigation time series, and analyze differences among the soils in effect of irrigation and cultivation on carbon sequestration. Results show that the effect of irrigation and cultivation on carbon sequestration varied with the soil. The same in irrigation and cultivation history, the five types of soils followed a decreasing order of Irrigated-alluvial soils> Fluvo-aquic soils >Fluvent soils > Aeolian sandy soil > Sierozem soil in SOCD. Irrigation and cultivation increased SOCD to a varying degree in these soils, which followed Aeolian sandy soil > Fluvo-aquic soils >Irrigated-alluvial soils> Sierozem soil > Fluvent soil. The differences among the soils in effect of irrigation and cultivation on carbon sequestration are significant in the Ningxia Irrigation Zone.