The　mechanical　properties　under　150°C　of　Al-4.5Mg-0.7Mn-0.1Zr　alloys　with　Er　addition　were　tested,　and　the　microstructure　were　analyzed　by　scanning　electrochemical　microcopy,　X-ray　diffraction　and　transmission　electron　microcopy.　It　showed　that　the　mechanical　properties　under　150°C　of　experimental　alloys　could　be　improved　greatly　by　trace　elements　Er　addition　with　the　elongation　keeping　stabilization.　It　was　found　that　the　Al3Er　particles,　which　formed　with　Er　addition,　were　nanophases　and　had　coherent　relationship　with　the　matrix.　At　the　same　time　Al3Er　particles　had　good　stability　and　no　aggregation　or　growing　up　under　the　experimental　temperature,　which　hindered　the　moving　of　dislocation　and　inhibited　the　course　of　recrystallizing,　thus　improving　the　high　temperature　mechanical　properties　of　experimental　alloys.