Two-dimensional　(2D)　chirality-induced　asymmetric　transmission/reflection　has　great　potential　for　polarization　applications.　Usually,　asymmetric　effects　resulting　from　circular　conversion　dichroism　(CCD)　occur　in　chiral　metasurfaces.　Here,　we　propose　a　single-layer　twisted　graphene-patterned　(with　tilted　elliptical　hole　arrays)　metasurface　and　theoretically　reveal　its　tunable　CCD　in　the　terahertz　(THz)　region.　The　unit　cell　of　the　metasurface　is　achiral.　Merely　by　altering　the　in-plane　orientation　of　holes　for　structural　2D　chirality,　a　tunable　CCD　can　be　achieved　at　normal　incidence.　Interestingly,　the　reflection　phase　can　be　consid-ered　an　intuitive　method　to　show　this　metasurface＇s　anisotropy,　which　complements　the　conventional　CCD　measurement　in　characterizing　chiral　materials.　Furthermore,　we　can　achieve　active　CCD　based　on　the　tunability　of　graphene.　Due　to　the　Fabry-Perot　resonance,　a　multiband　enhancement　of　CCD　spectrum　will　happen　by　changing　the　dielectric　layer　thickness.　The　proposed　metasurface　provides　more　flexible　opportunities　for　designing　active　THz　devices　for　polarization　manipulation.