In　this　letter,　combined　experimental　and　computational　analysis　has　allowed　new　understanding　of　the　vertical　material　flow　behaviors　during　friction　stir　welding.　It　is　found　that　a　high　-velocity　rotating　flow　zone　exists　near　the　welding　tool,　where　horizontal　and　vertical　flow　are　both　significant.　Material　entering　the　high　-velocity　rotating　flow　zone　migrates　to　the　lower　location　of　the　workpiece　after　multiple　rotations.　Material　outside　the　high　-velocity　rotating　flow　zone　bypasses　the　tool　and　migrates　towards　the　upper　locations.　The　findings　of　this　research　offer　insights　into　the　regulation　of　microstructures　and　the　formation　of　defects　in　FSW.