Abstract: The traditional reactive magnesium oxide (MgO) carbonation technology is an emerging soil stabilization method. However, since this technique requires CO₂ to be introduced at specific concentrations and pressures, it is challenging to control in practical engineering applications, often leading to uneven solidification, especially for clayey soils. To address this issue, the sodium bicarbonate (NaHCO₃) is used as a CO₂ carrier to treat the MgO-stabilized clay by an indirect carbonation method. The UCS, moisture content and XRD tests are conducted to investigate the effects of MgO and NaHCO₃ ratios, curing age, temperature and acidic conditions on the mechanical properties and expansibility of clay reinforced by the indirect carbonation. The results indicate that the UCS initially increases and then decreases with the addition of NaHCO₃, reaching its peak at an MgO: NaHCO₃ ratio of 2:1. With extended curing time and elevated temperatures, the strength generally increases. In terms of strength and anti-expansion performance, the MgO: NaHCO₃ ratio of 2:1 outperforms direct carbonation-stabilized soil. The XRD results show that the UCS of carbonated soil is mainly provided by hydromagnesite, or dypingite.