The properties of magnesium oxysulfate (MOS) cement with different granite powder (GP) contents with CO2 curing were studied. The hydration products and microstructure of MOS cement were conducted by X-ray diffraction (XRD), simultaneous comprehensive thermal analyzer (TG-DSC), scanning electron microscope (SEM) and mercury porosimeter (MIP). The results shows that: the strength retention coefficient of MOS cement containing 40% GP reaches 1.12 with standard curing 28 d and then in CO2 for 28 d; when MOS cement with CO2 curing 28 d and then immersion in water for 120 d, the strength retention coefficient reaches 0.94, which is 123.8% higher than blank samples; MgCO3·zH2O crystals generated after MOS cement with CO2 curing, which has a positive effect on mechanical properties and water resistance of that via reducing matrix expansion caused by MgO hydrated to Mg(OH)2; GP increases the matrix dense, reduces CO2 capture rate and decreases CO2 erosion of MOS cement by optimizing the pore structure; GP and MgCO3·zH2O improves the carbonation resistance and water resistance of MOS cement.