Sodium-ion　batteries　have　attracted　significant　recent　attention　currently　considering　the　limited　available　lithium　resource.　However,　the　energy　density　of　sodium-ion　batteries　is　still　insufficient　compared　to　lithium-ion　batteries,　mainly　because　of　the　unavailability　of　high-energy　cathode　materials.　In　this　work,　a　novel　sodium-rich　layered　oxide　material　(Na2MnO3)　is　reported　with　a　dynamical　stability　similar　to　that　of　the　Li2MnO3　structure　and　a　high　capacity　of　269.69　mA.h.g(1),　based　on　first-principles　calculations.　Sodium　ion　de-intercalation　and　anionic　reaction　processes　are　systematically　investigated,　in　association　with　sodium　ions　migration　phenomenon　and　structure　stability　during　cycling　of　Na(x)NnO(3)　(1　＜=　x　＜=　2).　In　addition,　the　charge　compensation　during　the　initial　charging　process　is　mainly　contributed　by　oxygen,　where　the　small　differences　of　the　energy　barriers　of　the　paths　2c　-＞　4h,　4h　-＞　2c,　4h　-＞　4h,　2c　-＞　2b,　and　4h　-＞　2b　indicate　the　reversible　sodium　ion　occupancy　in　transitional　metal　and　sodium　layers.　Moreover,　the　slow　decrease　of　the　elastic　constants　is　a　clear　indication　of　the　high　cycle　stability.　These　results　provide　a　framework　to　exploit　the　potential　of　sodium-rich　layered　oxide,　which　may　facilitate　the　development　of　high-performance　electrode　materials　for　sodium-ion　batteries.