Abstract: A new style stir head was designed to weld high strength aluminum alloy plate of 30mm thickness with friction stir welding.Microstructure and mechanical properties of friction stir welded joint of 7A05-T6 aluminum alloy thick plate were investigated.The results show that the dynamic recrystallization takes place in the weld nugget zone and fine grains are formed.Regarding to the thermo-mechanically affected zone on the sides,the advancing side consists of narrow slate grains,while the retreating side consists of flat and nubby grains.The adjusting range of process parameters is very narrow for welding of 30mm plate.When the rotating speed was 360 r/min and welding speed was 120 mm/min,the defect-free weld with good appearance was obtained,and the tensile strength of the weld reached 367.7 MPa,yield strength reached 280.8 MPa and the elongation reached 14.4%.Tensile strength of the weld could reach up to 95% of the base metal,and the elongation was higher than that of the base metal.