Abstract: The pre-cracked 6061-T4 aluminum alloy plate was repaired by friction stir method. The microscopic metallographic structure, tensile properties and hardness distribution of the two types of surface cracks and through-wall cracks were studied. The results show that the two pre-cracked specimens can be healed by friction stir repair under suitable welding parameters. Due to dynamic recrystallization, grain refinement in the repair zone forms fine equiaxed grains. The tensile strength of the sample after crack repair can reach 78 % of that of the base metal, and the elongation of the surface crack sample 16.1 %, the elongation of the through-crack specimen 14.2 %, which is ductile fracture; the distribution curve of microhardness in the crack repairing zone basically shows a "W" shape.