Abstract: The anodic oxidation method was adopted to prepare alumina film with two sorts of thickness on the surface of 7050 aluminum alloy, and then to weld by friction stir welding. The effect of surface oxidation film thickness on property of welded joints was studied. The results show that the effect of surface oxidation film thickness on property of welded joints was closely related to the welding parameters. When the thickness of oxidation film was 12.7 μm, welded speed was 50mm·min-1 and the rotation rate of stirring pin was 600-800 r·min-1, the tensile strength of joints was close to the joint of natural state surface. But when the thickness of oxidation film was 44 μm, the oxide content in weld seam raised and the tensile strength decreased prominently. The surface oxidation film increased the hardness of the welded core zone, the highest and lowest hardness value was 265 HV and 180 HV respectively when the film thickness was 44 μm.