Atomic　oxygen　(AO),　in　the　residual　atmosphere　of　low-Earth-orbit　space,　may　violently　collide　with　spacecraft　at　a　relative　speed　of　up　to　8　km/s　and　an　impact　energy　of　nearly　5　eV/atom.　These　collisions　can　lead　to　a　series　of　physical　and　chemical　reactions　that　may　result　in　increased　sputtering-erosion　and　corrosion　of　the　exposed　surface　with　performance　degradation.　This　work　examined　the　behavior　of　MoSi2,　a　commonly　used　coating,　when　exposed　to　AO　using　a　ground-based　space　environment　simulator.　The　erosion-corrosion　kinetics　and　evolution　of　the　microstructure　and　element　distributions　were　analyzed.　After　MoSi2　was　subjected　to　a　total　gas　fluence　of　9.72　×　1022　atoms/cm2　in　675　h,　the　erosion　yield　reached　an　exceptionally　low　value　of　10−28　cm3/atom,　indicative　of　its　superior　AO　resistance,　and　XRD,　SEM,　XPS　and　EPMA　were　applied　to　analyze　the　phase　transition　of　the　coating　surface:　first　it　was　released　of　adsorbed　gas　molecules　and　contaminants　on　the　coating　surface;　then　outside　Mo　and　Si　atoms　were　also　sputtered,　and　the　remaining　Mo　and　Si　atoms　were　gradually　oxidized;　finally,　a　continuous　protective　oxide　film　was　generated　which　effectively　resisting　AO　collisions.　After　AO　impact,　an　ultrathin　defensive　granular　oxide　layer　of　MoO3　and　SiO2　generated　from　the　original　smooth　MoSi2　coating.　Density　functional　theory　calculations　were　conducted　to　clarify　the　thermodynamic　and　electronic　structure　mechanisms　underlying　the　AO　oxidation　of　the　MoSi2　coating.　©　2024　Elsevier　Ltd　and　Techna　Group　S.r.l.