In order to solve the assembly gap problem in the process of friction stir welding for aluminum alloy of rail car body,this paper adopts the method of filling welding wire and welding pad in the gap to carry out friction stir welding of 6082-T6 aluminum alloy. It was found that the fracture posi-tion located at heat affect zone for the tensile specimens of both FSW joints. The filling of welding wire and welding sheet did not cause crack formation in weld nugget and further affect the mechanical properties. Moreover,increasing the welding speed was helpful to improve the tensile strength of FSW joints with adding welding wire and welding sheet. A high ultimate tensile strength（UTS）of 245 MPa was obtained in the FSW joint with adding welding sheet under an optimal parameter of 1200 r/min and 600 mm/min;while the UTS reduced to 235 MPa for FSW joint with adding welding wire. This study provides an efficient method to solve the assembly gaps in the FSW of long Al alloy welds.