Magnesium slag is a by-product of the magnesium industry. As an auxiliary cementitious material incorporated into concrete, it can make full use of waste resources and has a certain potential for hydration and carbonation. To improve the mechanical properties of the concrete, the influence mechanism and strengthening mechanism of the carbon curing method on mechanical properties of magnesium slag concrete were investigated. The effects of different magnesium slag content and water-cement ratio on mechanical properties and ecological properties of carbon cured magnesium slag concrete were analyzed. Based on the phase composition and thermogravimetric composition of magnesium slag concrete, the carbonation mechanism of magnesium slag was revealed. The mechanical properties models of magnesium slag concrete with different carbon curing were constructed. The study shows that with the increase of the magnesium slag, the mechanical properties of carbon curing concrete first increase and then decrease. The optimum mechanical properties of concrete are 30% magnesium slag, and the compressive strength reaches 42.3 MPa. The content of magnesium slag increased from 0% to 60%, and the carbon fixation content was 14.60%, 11.87%, 11.69%, 16.90%, 19.80%, 14.78%, and 13.09%, respectively. With the increase of magnesium slag content, the content and grain size of magnesium oxide in concrete increase, which leads to more micro-bumps and depressions on the surface of the concrete structure. The hydration reaction and carbonation reaction of gelled materials are affected by magnesium ions, resulting in changes in the morphology and crystal structure of CaCO₃ and MgCO₃ reactants.