Carbon-based　nanomaterials　such　as　graphene　oxide　sheetreinforced　cementitious　composites　have　attracted　extensive　interest　owing　to　their　improved　post-fire　mechanical　properties.　However,　the　role　of　graphene　in　anti-thermal　detriment　is　still　unclear.　In　the　current　study,　the　mechanical　characteristics,　pore　structure,　and　interface　evolution　of　graphene-toughened　cementbased　materials　under　high　temperatures　are　investigated.　Scanning　electron　microscope　analysis　showed　that　graphene　implanted　in　the　cement　matrix　had　out-of-plane　deformation　at　elevated　temperature.　The　deformation　caused　the　evolution　of　the　interface　between　graphene　and　the　cement-based　material　with　respect　to　temperature.　Correspondingly,　the　toughening　effect　of　graphene　on　cement-based　materials　decreased　first　and　then　increased.　The　reinforced　domain　of　graphene　switched　from　mesopores　to　capillary　pores　when　the　temperature　was　beyond　400　degrees　C,　contributing　to　the　enhanced　reinforcement　efficiency　of　the　cement　mortar.　The　interfacial　evolution　process　with　an　in-depth　analysis　based　on　multiple　scales　would　benefit　from　optimizing　the　design　of　graphene　composites　at　high　temperatures.