Abstract: Joints of 35 mm thickness 6005A-T6 aluminum alloy by friction stir welding on both sides were obtained,and formation of weld is well and there are no defects such as tunnel defect,hole and groove defect,etc.Microstructures and properties of weld joint by friction stir welding have been studied by scanning electron microscope optical microscope and electron and tensile testing machine.Experimental results show that equiaxial crystal is formed in weld nugget zone,visible spiricle and clear comb line are formed in advancing side,and the grains are elongated and banded structuree are formed in thermal-mechanical affected zone,coarse grains are formed in heat affected zone;The fine crystal grains are formed and there are no spiricle in transition zone of retreating side.The tensile strength reached 213 MPa at rotation speed of 650 r/min and welding speed of 200 mm/min,and the tensile strength reaches 84.8% of base metal.Fracture occurred in heat affected zone of advancing side;The lowest microhardness is about 50 HV which is in heat affected zone of advancing side.