An　unconditionally　stable　FDTD　method　is　proposed　in　this　paper　to　simulate　graphene.　By　transforming　the　third-order　equation　of　the　electric　field　to　the　first-order　equation　and　applying　the　backward-difference　discretization　to　the　time-derivation,　the　time　step　size　can　be　selected　arbitrarily.　Both　the　theoretical　analysis　and　numerical　example　validate　the　unconditional　stability　of　this　method.　The　simulation　of　the　infinite　graphene　sheet　also　shows　that　as　long　as　the　time　step　size　is　chosen　satisfied　the　accuracy　requirement,　this　proposed　method　can　observably　speed　up　the　whole　simulation　with　high　accuracy,　even　the　time　step　discretization　is　orders　of　magnitude　larger　than　that　permitted　by　the　CFL　condition.　©　2020　IEEE.