The　fatigue　failure　rule　of　7075-T651　aluminum　alloy　stir　welded　joint　is　studied　under　two-stage　variable　amplitude　loading　by　fatigue　experiments　and　finite　element　simulation.　The　results　show　that　the　friction　stir　welding　(FSW)　joints　have　different　weak　areas　under　different　loading　conditions.　The　fracture　position　of　the　FSW　joint　is　related　to　the　loading　sequence　of　variable　amplitude　load　and　cycle　number.　The　cycle　number　and　crack　length　under　the　first-stage　loading　influence　the　fatigue　life　and　fracture　location　of　the　FSW　joints.　When　the　cycle　ratio　of　the　first-stage　loading　is　70　~　80%,　the　fracture　position　of　the　corresponding　specimen　does　not　change.　The　simulation　results　show　that　the　corresponding　cycle　ratios　of　critical　damage　under　low–high　load　and　high-low　load　are　77.8%　and　74.4%,　respectively,　which　are　consistent　with　the　experimental　results.　When　the　crack　length　is　greater　than　400 μm　under　low–high　load,　or　when　the　crack　length　is　greater　than　500 μm　under　high-low　load,　the　crack　location　does　not　change.　©　International　Institute　of　Welding　2024.