The　welding　process　parameters　of　dissimilar　2024-T4　and　7075-T6　aluminum　alloy　friction　stir　welded　(FSWy)　joints　are　selected　by　the　metallographic　microstructure,　the　mechanical　properties,　and　the　hardness　distribution.　The　joints　with　rotational　speed　of　900　rpm　and　advancing　speed　of　100　mm/min　that　have　the　highest　tensile　strength　are　used　to　carry　out　the　experimental　fatigue　research.　The　short　crack　growth　behavior　of　dissimilar　FSW　joints　is　analyzed　through　the　replica　technique.　The　stage　of　the　crack　initiation　and　stable　growth　accounts　for　about　60　similar　to　80%　of　total　fatigue　life.　The　short　crack　grows　rapidly　once　it　reaches　the　crack　size　of　approximately　350　similar　to　450　mu　m.　The　cracks　are　prone　to　initiate　at　the　defects　of　subsurface　in　the　weld　nugget　zone　and　propagate　in　a　quasi-cleavage　fracture　mode.