In this paper,the welding parameters in friction stir welding of 6005 A-T6 Al alloy extrusions used in side wall of metro train were optimized. Based on the welding parameter window with rotational speed of 1000-2100 r/min for and welding speed of500 ,2, 200 mm/min obtained in preliminary experiments,a spindle speed of 1 500 r/min and welding speed of 1 100 mm/min were determined as the optimal parameters via comparing the appearing quality of welding seam. Metallographic analysis and tensile and bending tests were performed for joints welded with different axial forces. With a spindle speed of 1 500 r/min,welding speed of 1 100 mm/min and axial force of 13.5 k N,defect free joints could be obtained,while the tensile strength reached 80% of base metal and no fracture occurred in 180° bending tests.