Corrosion　is　the　main　factor　affecting　the　service　performance　of　reinforced　concrete　(RC)　structures,　especially　in　offshore　or　coastal　areas.　In　this　paper,　taking　RC　beam　as　the　research　object,　a　three-dimensional　meso-scale　numerical　model　involving　rebar　corrosion　was　established.　The　corrosion　effects　on　the　mechanical　behavior　of　RC　beam　was　explored　through　a　multi-stage　analysis　method　(namely,　corrosion　induced　expansion　stage　and　structural　deterioration　stage).　The　non-uniform　radial　displacement　was　applied　to　concrete　around　the　steel　to　simulate　the　expansion　of　rebar　corrosion.　The　cracking　process　and　the　damage　pattern　of　concrete　caused　by　corrosion　can　be　obtained.　Then,　taking　this　state　as　the　initial　condition,　the　mechanical　analysis　of　corroded　RC　beam　was　carried　out.　The　agreement　between　the　numerical　and　the　test　results　validates　the　rationality　and　correctness　of　the　multi-stage　analysis　model.　According　to　the　simulation　results,　the　concrete　damage　due　to　corrosion　is　mainly　concentrated　in　the　diagonal　of　reinforcement　and　the　middle　of　adjacent　reinforcement.　The　rust　expansion　pressure　increases　gradually　when　the　corrosion　level　increased.　For　severely　corroded　beams,　the　concrete　strain　no　longer　conforms　to　the　plane　section　assumption.　In　addition,　corrosion　reduces　the　bearing　capacity　and　ductility　of　the　beams.　The　coupling　effects　of　corrosion　of　tensile　and　compression　bars　on　the　performance　of　the　beam　are　more　serious　than　that　of　only　corrosion　of　tensile　bars.　Based　on　the　data　regression,　a　relationship　to　evaluate　the　bearing　capacity　of　beams　was　established.　It　indicates　that　the　flexural　bearing　capacity　decreases　by　about　1.4%,　1.7%　annually　in　the　conditions　of　tensile　reinforcement　corroded　only　and　both　tensile　and　compressive　reinforcement　corroded.