Addition of quartz sand to Portland cement can prevent its mechanical properties from declining due to crystal transformation at high temperatures. However，the composition and morphology changes of hydration products of sand-coated cement under the combined action of 180 ℃ and supercritical CO₂ are more complex，so the effect of high temperature CO₂ on the mechanical properties of cement is still unclear. Therefore，the corrosion depth，pore size distribution，mechanical properties， phase composition，functional groups and microstructure of cement stone in supercritical CO₂ environment at 180 ℃ were analyzed by means of scanning electron microscopy，mercury injection，thermogravimetric analysis，X-ray diffraction test and infrared spectrum characterization. The results showed that with the increase of corrosion time，the corrosion depth of cement stone increased，the compressive strength decreased，and the porosity decreased first and then increased. The hydration products were composed of acicular xonotlite（C₆S₆H），columnar hillebrandite（C₂SH），sheet and rod-shaped calcium carbonate（CaCO₃）and loose porous amorphous SiO₂. Under the condition of supercritical CO₂ at 180 ℃，the influence mechanism of hydration product evolution of cement on its performance was obtained as follows. In the early stage of corrosion，a large amount of C₂SH and a small part of C₆S₆H were corroded to generate CaCO₃ and amorphous SiO₂. CaCO₃（mainly aragonite and vaterite）would fill part of the pores，while the polymerization degree of C-S-H gel increased，slowing down the carbonization corrosion rate. In the later stage of corrosion，the increase of calcite content could promote the development of strength to a certain extent. But with the progress of corrosion，the vaterite and aragonite dissolved，a large number of C₆S₆H were corroded and then the morphology changed toward flake and block，resulting in the increase of porosity of cement stone，the decrease of polymerization degree of C-S-H gel and compressive strength，and the acceleration of carbonization. Under supercritical CO₂ at 180 ℃，the evolution of C-S-H gel（C₆S₂H and C₆SH）and calcium carbonate（calcite，aragonite and vaterite）determined the change of mechanical properties of Portland cement.