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°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.　©　2024,　American　Concrete　Institute.