Abstract: The sulfate-bearing (saline) soil may easily cause geotechnical disasters, such as subsidence, expansion and foundation corrosion. However, stabilizing the sulfate-bearing soil by cement can lead to the formation of expansive mineral-ettringite, resulting in soil swelling, strength loss and poor durability. To avoid the aforementioned problems, the magnesium oxide (MgO) is used to partially replace cement (MgO combined with cement) in the stabilization treatment of the sulfate-bearing soil (gypseous soil). By conducting the tests of vertical swelling, unconfined compressive strength (UCS), X-ray diffraction (XRD), scanning electron microscopy (SEM) and nuclear magnetic resonance (NMR), the effects of the ratio of MgO to cement on the swelling and mechanical properties of the stabilized soil are explored. Furthermore, it reveals the micro-mechanism of the sulfate-bearing soil stabilized with MgO and cement (MgO-cement). The results show that as the ratio of MgO to cement increases, the total swelling percentage of the stabilized soil first decreases and then increases, while the UCS has an opposite trend, first increasing and then decreasing. In terms of the micro-mechanism, the addition of an appropriate amount of MgO can reduce the formation of ettringite. However, when an excess of MgO is added, the formation of magnesium silicate hydrate (MSH) inhibits the formation of calcium silicate hydrate (CSH), thereby weakening the effects of CSH. In summary, MgO: cement= 0.5∶9.5 is considered to be an optimal ratio of MgO to cement for stabilizing the sulfate-bearing soils.