Abstract: To reduce carbon emissions and explore carbon dioxide (CO₂) utilization technologies in geotechnical engineering, this study proposes a novel method for preparing carbon sequestration lightweight soil (C-LS) based on the magnesium oxide (MgO) carbonation mechanism. A mixture of MgO and waste soil is used as a binder instead of cement and CO₂ instead of air for foaming. By mixing MgO, silty clay, water and CO₂ foam in specific proportions, C-LS with a density of less than 1 g/cm³ is formed. Through unconfined compressive strength tests, scanning electron microscopy (SEM) and thermogravimetric analysis (TGA), the effects of MgO proportions, designed wet densities, water-to-solid ratios and carbonation curing conditions on the fluidity, setting time, dry density, strength, carbonation products and carbon sequestration capacity of C-LS are studied. The results show that with the increase of MgO proportion and wet density, the fluidity and setting time of C-LS decrease, while the strength and carbon sequestration efficiency improve. The optimal mix proportion of C-LS is determined, ensuring that under ambient conditions, its 28-day strength meets the requirements for highway embankment filling and other backfill applications. Under accelerated carbonation conditions, the strength of C-LS can be further improved. Based on the intrinsic relationship between the strength of C-LS, the amount of carbonation product, and the carbon sequestration rate, the study reveals the strength formation mechanism of C-LS and proposes a microscopic model. The C-LS technology can significantly