In　addition　to　the　normal　service　loadings,　engineering　structures　may　be　subjected　to　occasional　loadings　such　as　earthquakes,　which　may　cause　severe　destruction.　When　the　steel　rebar　is　corroded,　the　damage　could　be　more　serious.　To　investigate　the　seismic　performance　of　corroded　RC　columns,　a　three-dimensional　mesoscale　finite　element　model　was　established.　In　this　approach,　concrete　was　considered　as　a　three-phase　composite　composed　of　aggregate,　mortar　matrix　and　interfacial　transition　zone　(ITZ).　The　nonlinear　spring　were　used　to　describe　the　bond　slip　between　steel　and　concrete.　The　degradation　of　the　material　properties　of　the　steel　rebar　and　cover　concrete　as　well　as　the　bonding　performance　due　to　corrosion　were　taken　into　account.　The　rationality　of　the　developed　numerical　analysis　model　was　verified　by　the　good　agreement　between　the　numerical　results　and　the　available　experimental　observation.　On　this　basis,　the　effect　of　corrosion　level,　axial　force　ratio　and　shear-span　ratio　on　the　seismic　performance　of　corroded　RC　columns,　including　lateral　bearing　capacity,　ductility,　and　energy　consumption,　were　explored　and　discussed.　The　simulation　results　indicate　that　the　mesoscopic　method　can　consider　the　heterogeneity　of　concrete,　to　more　realistically　and　reasonably　reflect　the　destruction　process　of　structures.