Manganese-based　(Mn-based)　layered　oxides　have　emerged　as　competitive　cathode　materials　for　sodium-ion　batteries　(SIBs),　primarily　due　to　their　high　energy　density,　cost-effectiveness,　and　potential　for　mass　production.　However,　these　materials　often　suffer　from　irreversible　oxygen　redox　reactions,　significant　phase　transitions,　and　microcrack　formation,　which　lead　to　considerable　internal　stress　and　degradation　of　electrochemical　performance.　This　study　introduces　a　high-entropy　engineering　strategy　for　P2-type　Mn-based　layered　oxide　cathodes　(HE-NMCO),　wherein　a　multi-ingredient　cocktail　effect　strengthens　the　lattice　framework　by　modulating　the　local　environmental　chemistry.　This　innovative　approach　fosters　sustainable　reversible　oxygen　activity,　mitigates　stress　concentrations　at　grain　boundaries,　and　accelerates　Na+　transport　kinetics.　The　resulting　robust　lattice　framework　with　optimized　elemental　interactions　significantly　improves　structural　integrity　and　reduces　the　formation　of　intragranular　fractures.　Consequently,　HE-NMCO　demonstrates　remarkable　cycling　stability,　retaining　93.5　%　capacity　after　100　deep　(de)sodiation　cycles,　alongside　an　enhanced　rate　capability　of　134.1　mAh　g-1　at　5　C.　Notably,　comparative　studies　through　multimodal　characterization　techniques　highlight　HE-NMCO　＇　s　superior　reversibility　in　oxygen　anion　redox　(OAR)　reactions　over　extensive　cycling,　contrasting　sharply　with　conventional　NMCO　cathode.　This　work　elucidates　the　potential　for　advancing　high　energy　and　power　density　Mn-based　cathodes　for　SIBs　through　local　species　diversity.