The　physical　and　mechanical　properties　of　graphene-reinforced　epoxy　(epoxy/graphene)　in　hygrothermal　environment　need　to　be　comprehensively　understood.　This　is　because　it　is　necessary　to　predict　the　durability　of　epoxy/graphene　when　epoxy/graphene　is　used　in　an　aggressive　environment　with　high　humidity　and　high　temperature.　Based　on　the　molecular　dynamics　method,　the　influences　of　water　content　(2,　4　and　6%)　and　temperature　(298,　333　and　368　K)　on　the　physical　and　tensile　properties　of　epoxy/graphene　were　studied　in　this　research.　The　results　showed　that　after　the　addition　of　graphene,　the　free　volume　fraction　of　epoxy　and　the　diffusion　coefficient　of　water　molecules　in　the　epoxy　decreased,　and　the　density,　tensile　strength　and　deformation　performance　of　epoxy　increased.　In　the　hygrothermal　environment,　the　tensile　strength　degradation　rate　of　epoxy/graphene　was　lower　than　that　of　pure　epoxy.　The　failure　mechanism　and　mechanical　response　of　epoxy/graphene　during　the　tensile　process　in　the　nanoscale　were　revealed.　The　research　results　provide　a　reference　for　the　design　and　performance　optimization　of　epoxy/graphene　composites　in　a　hygrothermal　environment.