Carbon　nanotube　(CNT)-reinforced　poly　(methyl　methacrylate)　(PMMA)　composite　is　subjected　to　changing　temperature　levels　when　used　in　aerospace　field,　which　leads　to　the　morphing　structure　and　changing　properties,　and　even　structural　failure.　In　this　paper,　the　temperature　effect　on　the　structure　and　properties　of　PMMA/CNT　nanocomposite　with　different　CNT　volume　fractions　is　investigated　using　molecular　dynamics　(MD)　simulation.　It　is　measured　that　with　increasing　temperature　from　100　to　500　K,　the　longitudinal,　transverse,　and　shear　moduli　of　PMMA/CNT　nanocomposite　decrease　by　30　%,　45　%,　and　62　%,　respectively,　while　the　coefficient　of　thermal　expansion　(CTE)　increases　by　27　%.　It　is　found　that　the　atom　distribution　becomes　more　dispersed　and　the　nanocomposite　structure　turns　to　looser,　which　lead　to　the　weakened　properties　of　the　nanocomposite.　Based　on　the　MD　results,　the　efficiency　parameters　of　PMMA/CNT　nano　-composite　are　derived　using　extended　rule　of　mixtures　(EROM),　which　are　used　to　predict　the　mechanical　properties　of　nanocomposite　at　different　temperatures.　The　revealed　temperature　-dependent　mechanical　properties　and　the　underlying　mechanisms　contribute　to　the　understand-ing　of　performance　changes　of　PMMA/CNT　nanocomposite　under　the　temperature　effect,　which　provide　references　for　the　application　of　composite　materials　in　the　aerospace　field　where　the　changing　temperatures　are　of　highly　concern.