The microstructure and stress corrosion resistance of 6005 A-T6 aluminum alloy joints by friction stir welding were studied using optical microscope,scanning electron microscope and four points bending stress corrosion methods. The results show that the hardness distribution of the joint is W-shape,the lowest hardness appears at the heat affected zone,and the hardness is improved at the weld nugget zone,and the highest hardness appears at the base metal. The main strengthening phase of the base metal is Q’ phase,most of which is disappeared at the weld nugget zone,and where exists lots of dislocation and the main strengthening mechanism is fine grain strengthening,dislocation strengthening and solid solution strengthening. Friction stir welded joint shows good stress corrosion resistance,however corrosive pitting is also happened,and the weakest part of the welded joint is in the heat affected zone.