Protective　effects　of　the　atmosphere　of　FeS　2　and　HFC-134a　mixed　with　air　on　magnesium　alloy　melted　in　a　sealed　melting　furnace　were　analyzed.　The　results　show　that　the　atmosphere　of　air　containing　both　sulphur　and　fluorine　has　a　good　protective　effect　on　magnesium　alloy　melting,　and　with　the　same　melting　temperature　and　holding　time,　it　is　better　than　that　containing　only　sulphur　or　fluorine.　The　atmosphere　with　0.15%　HFC-134a　and　1　g　FeS　2　can　prevent　magnesium　melt　from　oxidation　and　combustion　at　730°C　for　1　min　to　30　min.　However,　holding　for　60　min　at　730°C,　the　atmosphere　is　failure.　The　characteristics　of　the　surface　film　formed　at　controlled　condition　was　analyzed　by　SEM,　EDS　and　XRD.　The　protective　films　formed　in　the　atmosphere　of　air　containing　both　sulphur　and　fluorine　contain　Mg,　F,　O　and　S,　and　the　basic　phases　are　MgF　2,　MgO　and　MgS.　With　the　increase　of　holding　time,　the　surface　film　exhibits　more　homogeneous,　denser　and　thicker　due　to　the　increase　of　MgF　2　and　MgS　in　the　MgO-based　oxide　film.