Medium　Mn　advanced　high　strength　steel　(AHSS)　with　significant　combination　of　strength　and　ductility　is　one　of　candidates　of　the　Third　Generation　AHSS.　However,　the　specific　plastic　instability　behavior　of　medium　Mn　steels　is　different　from　traditional　steels　and　physical　mechanism　behind　it　is　unclear.　Representative　volume　element　(RVE)　has　been　proved　to　be　applicable　of　describing　microstructural　deformation　and　revealing　the　micro-deformation　mechanism.　In　this　paper,　a　two　dimensional　micro-mechanical　RVE　of　medium　Mn　steel,　7MnCA,　is　constructed　from　its　electron　back　scatter　diffraction　(EBSD)　data.　The　deformation　behavior　under　uniaxial　tension　is　investigated　based　on　the　constructed　RVE　models　incorporating　with　phases　morphology　and　distribution.　The　results　show　that　the　present　RVEs　constructed　from　EBSD　data　through　image-processing　algorithm　with　different　filling　strategies　are　capable　to　predict　the　macroscopic　mechanical　behavior　of　medium　Mn　steel　with　finite　element　analysis.