Thermodynamic　equilibrium　phases　of　Al-Mg　alloy　with　minor　Sc　contents　and　effects　of　chemical　compositions　on　the　equilibrium　phases　were　researched　by　means　of　Miedema　model　and　MTDATA　software　as　well　as　the　related　databases　of　the　general　Al　alloy.　The　possible　thermodynamic　equilibrium　phases　were　analyzed　through　the　MTDATA　and　compared　with　the　results　of　the　calculation　through　the　Miedema　model.　The　related　phase　transformation　was　discussed,　the　formation　enthalpy　(-35.11　kJ/mol)　of　Al3Sc　phase　was　calculated　and　the　Al3Sc　phase＇s　precipitation　and　stability　until　900　K　was　studied　and　verified,　which　can　be　used　to　explain　experiments　phenomena　of　relevant　alloys　and　is　beneficial　to　the　real　Al-Mg　alloy　series　strengthened　and　application.