To　study　the　strengthening　effect　and　mechanism　of　Er　element　on　the　weld,　the　remelting　welding　of　Al-Mg　alloy　with　Er　was　adopted,　and　the　organizational　structure　and　mechanical　properties　of　the　joint　were　observed.　The　results　show　that　there　is　primary　Al3Er　phase　precipitation　on　the　grain　boundaries　in　weld,　but　the　quantity　of　it　is　fewer　than　that　of　in　the　base　material,　and　the　precipitation　doesn＇t　form　a　continuous　ring.　The　secondary　Al3Er　precipitation　also　can　be　found　in　the　welding,　but　the　precipitation　phase　quantity　is　very　few.　Er　elements　will　presence　in　the　solid　solution　or　segregation　way.　The　strength　of　Er　element　on　the　weld　joint　is　mainly　based　on　the　primary　Al3Er　to　refine　the　grain.　The　effect　of　the　secondary　phase　on　the　weld　joint　is　small,　and　so　the　weld　joint　mechanical　properties　decrease　evidence.　The　tensile　strength　of　welded　joints　is　297　MPa,　and　the　strength　coefficient　of　welded　joints　is　72%　of　base　material.　Tensile　fracture　position　is　mainly　in　the　center　of　the　weld　and　near　the　fusion　zone.