Large　rupture　strain　(LRS)　FRPs　have　great　potential　to　be　used　for　seismic　retrofit　of　RC　columns　because　of　its　high　rupture　strain　(i.e.,　＞　5%)　that　provides　better　confinement　effects.　However,　in　FRP-confined　RC　columns,　the　longitudinal　reinforcements　may　buckle　before　the　LRS　FRP　rupture,　especially　in　the　case　of　large　stirrup　spacing.　This　study　aims　to　present　a　3D　finite　element　(FE)　model　for　simulating　the　buckling　effect　of　longitudinal　reinforcements　in　LRS　FRP-confined　RC　columns.　A　modified　concrete　damaged　plasticity　model　(CDPM)　is　proposed　to　consider　the　deformation　and　mechanical　characteristics　of　LRS　FRP-confined　concrete.　Removal　of　failed　concrete　elements　is　considered　to　facilitate　the　buckling　of　longitudinal　reinforcements　in　LRS　FRPconfined　RC　columns.　The　FE　analysis　accuracy　was　verified　by　comparisons　with　test　results.　The　factors　affecting　the　buckling　of　longitudinal　reinforcements　were　discussed　through　an　extensive　parametric　study.　Empirical　formulas　for　the　stress　and　strain　values　at　which　the　longitudinal　reinforcement　starts　to　soften　were　developed.　An　empirical　formula　for　the　ultimate　axial　strain　of　LRS　FRP-confined　RC　columns　determined　by　longitudinal　reinforcement　buckling　was　also　obtained　by　regression　analysis.