Abstract：For refill fiction stir spot welding, voids and lack of fill defects induced by insufficient material flow are easily formed at the maximum plunging position of sleeve and the movement path of sleeve. The geometry of sleeve is the main factor influencing the material flow during welding. In this paper, the outside wall of sleeve with inclined grooves were designed. On basis of the verification of rightness of finite element model by experiments, the effect of groove on material flow behavior was investigated by numerical simulation. The results show that the inclined groove can heighten the material downward flow velocity. With the increase of groove width, the material downward flow velocity decreases and the material high-speed flow area increases. When the groove width is 0.75mm, the sleeve has the most obvious effect on promoting the downward flow of material.