This work developed a friction-stir-welding system for thin wall pipes and realized high performance Al/Cu pipe joining.Five kinds of intermetallic compounds（IMCs） with different characteristics has been found through macro-/micro-scale observation.The contents of IMCs have been detected to be Al,2,Cu,Al,4,Cu,9, and AlCu（small amount） through X ray diffraction and nanoindentation.Different shear effect and pressure effect by welding tool were found to be the main formation mechanisms of different kinds of IMCs through further research and analysis.