The invention provides a method for eliminating a keyhole-free friction stir spot welding ring groove. According to the method, through zero point setting before welding, the length of the part, stretching out of a datum plane, of a stirring pin is 10% of the thickness of a to-be-welded base material, the length of the part, stretching out of the datum plane, of a stirring sleeve is 80% of the stretching length of the stirring pin, and at this moment, the positions of the stirring pin and the stirring sleeve are set as zero points, that is, the zero points are determined by a numerical controlsystem; and before a stirring tool moves downwards, the stirring pin and the stirring sleeve are drawn back at the same time. After the stirring pin and the stirring sleeve are welded and return to the original point, the stirring pin continues to move downwards; and when the quantity that the stirring pin continues to move downwards is 20% of the thickness of the base material, the stirring pinis kept at the position to rotate for 1 s to 2 s, aluminum metal in a molten state is fully backfilled to the position around the welding point, the stirring pin and the stirring sleeve return to theoriginal point and rotate for 1 s to 5 s, the periphery of the welding point is fully filled with the aluminum metal in the molten state, and the aim of eliminating the welding defect ring groove is achieved. The method is used for welding of aluminum plates of 1 mm, 2 mm, 3 mm, 4 mm and 5 mm, and the welding ring groove defect is eliminated.