Abstract: A professional friction stir welding simulation software MORFEO was used to observe flow characteristics of different thickness. 2024 aluminum alloy sheets of 4 mm thickness were butt jointed. Two local 3D models of two kinds of pin profiles were set up, namely cylindrical and conical shapes. Compared with other simulation software, MORFEO provided a more convenient and parameterized way to demonstrate each level's streamlines and gave a quasi steady state description of the material deposition which helped to predict defects caused by insufficient flow. The material close to the shoulder tended to move farther around the pin. Both sides' material flowed around the pin to the retreating side behind the moving pin and lefe large vacant space on the advancing side. Whereas when the pin was tapered and had an appropriate rotation speed such as 600 r/min in this paper, the material could be taken to both sides behind the pin on each level. Similar results had also been observed in the experiment conducted with the marker technique.