Fatigue　properties　of　friction　stir　welding　(FSW)　butt　joints　for　Al-Cu　alloy　2219-T6　were　investigated　by　experimental　analysis　and　numerical　simulation.　Microstructure　characteristics　of　FSW　butt　joints　for　2219　aluminium　alloy　were　studied　during　different　fatigue　stages.　Micro　hardness　values　and　grain　sizes　across　the　FSW　joint　at　different　cycles　were　measured　to　study　the　fatigue　properties　of　the　joint.　Local　mechanical　performances　of　the　FSW　butt　joints　were　investigated　based　on　the　micro　tensile　tests.　Fatigue　parameters　of　different　regions　in　the　FSW　joints　were　obtained　from　the　four-point-correlation　method.　The　local　stress　and　strain　response　of　the　FSW　joints　were　obtained　based　on　mechanical　performances　of　the　micro　tension　specimens.　The　comparison　results　between　simulation　and　tests　analysis　show　that　the　built　finite　element　model　is　effective　for　estimating　the　weak　areas　for　FSW　joints.