A　novel　material　tracing　technology　was　proposed　using　ER2319　aluminium　alloy　welding　wire　as　the　tracer　material　to　study　the　material　flow　behaviour　at　different　positions　of　friction　stir　welded　6061-T6　aluminium　alloy　joint.　Having　been　influenced　by　temperature　and　driving　force　of　the　tool,　the　displacement　of　all　the　tracer　materials　deposited　behind　the　original　position　during　welding　decreased　gradually　from　top　to　bottom　of　the　stir　zone　(SZ).　The　advancing　side　(AS)　and　the　retreating　side　(RS)　of　the　SZ　are　dominated　by　the　shear　action　and　the　extrusion　action,　respectively.　The　extrusion　force　and　friction　force　are　the　driving　forces　for　material　flow　during　friction　stir　welding.　The　material　flowed　downward　at　the　AS　and　upward　at　the　RS　in　the　vertical　plane　of　the　joint,　while　the　material　of　the　SZ　flowed　to　the　back　of　the　tool　through　the　RS　in　all　the　horizontal　planes　of　the　joint.　The　flow　path　of　tracer　material　in　most　positions　of　the　SZ　is　arc　shaped,　however,　it　is　a　complex　curve　in　the　SZ　bottom　at　the　AS　due　to　the　poor　material　flowability.　The　rotation　angle　of　the　tracer　material　decreased　from　AS　to　RS　of　the　SZ　and　from　top　to　bottom　of　the　SZ.