A thermal-mechanical coupling model of whole FSW process of 6061 Al alloy sheet is established based on the solid mechanics theory. Material flow behavior of whole FSW process is studied by using arbitrary Lagrangian-Eulerian（ALE）mesh adaptive technique and particle tracking technique. The results show that the material around the stir zone moves to the back of the stir head mainly in the form of rotating flow and laminar flow. The material on the upper surface has a tendency to move downward spirally affected by the shoulder whereas the material in middle part first moves in a spiral upward mode affected by the pin and then moves downward. Near the bottom of the weldment,metal material moves to the back of stir head mainly in the form of laminar flow.