The　alternating-direction-implicit　finite-difference　time-domain　(ADI-FDTD)　method　is　modified　to　simulate　a　graphene-based　frequency　selective　surface.　By　using　the　auxiliary　differential　equation　and　Pade　fitting　method,　both　the　interband　and　intraband　conductivity　of　the　graphene　are　incorporated　into　the　ADI-FDTD　method.　The　ADI-FDTD　method　has　excellent　computational　accuracy　and　its　computational　efficiency　is　considerably　improved　from　that　of　the　conventional　FDTD　method.　By　using　the　proposed　ADI-FDTD　method,　a　graphene-based　frequency　selective　surface　is　simulated　and　analyzed　at　terahertz　frequency.　The　numerical　results　show　that　the　graphene　can　achieve　a　tunable　frequency　selective　surface　through　controlling　its　chemical　potential,　and　the　interband　conductivity　of　the　graphene　has　important　effect　on　the　performance　of　the　frequency　selective　surface.