Based　on　the　binary　phase　diagrams　of　Al-M(M=Sr,　Nd),　Miedema　model　and　Toop　model,　the　thermodynamic　calculation　model　for　predicting　the　precipitation　behaviors　of　the　Al-M　intermetallic　compounds　in　Mg-Al-M　system　was　deduced.　The　calculated　precipitating　temperature　of　Al-Sr　compound　in　Mg-8Al-3.5Sr　ternary　system　is　in　good　agreement　with　the　references.　The　lowest　contents　of　M　in　the　Mg-9/6Al-M(M=Sr,　Nd),　making　the　Al-M　compounds　precipitate　prior　to　alpha-Mg,　were　calculated,　the　precipitation　behaviors　of　the　Al-M　compounds　and　their　effects　to　the　mechanical　properties　of　Mg　alloys　were　discussed.　Composite　addition　of　Nd　and　Sr　to　prepare　the　heat　resistance　of　Mg　alloys　with　higher　strength　was　proposed.