The　intergranular　corrosion　and　stress　corrosion　cracking　resistance　of　Al-Zn-Mg-Cu　alloy　with　trace　Er　addition　were　studied　by　means　Of　Such　methods　as　stress　corrosion　cracking　and　intergranular　corrosion　test　in　GB-T7998-2005　and　HB5254-83.　The　microstructures　were　observed　by　optical　microscope　and　scanning　electron　microscope　(SEM).　The　results　show　that　alloys　with　trace　Er　addition　have　been　improved　on　intergranular　corrosion　and　stress　corrosion　cracking　resistance,　but　corrosion　resistance　of　alloys　can　be　descending　when　Er　addition　exceed　0.4%.