The invention relates to an aluminum alloy welding method which comprises the following steps: (1) carrying out back welding to to-be-welded areas of two panels by means of direct current tungsten electrode inert gas shielded-arc welding, wherein the to-be-welded areas of the two panels are not grooved to form back weld joints; and (2) carrying out cosmetic welding at least one time to the back weld joints and areas close to the back weld joints by means of cold metal transition welding to form cap welds so as to finish welding. Therefore, the method can improve the tensile property of the aluminum alloy welding head, and the strength coefficient of the welding head is 70% or over.