The invention discloses a method for adding an intermediate welding material to improve strength of an aluminum-lithium alloy welding joint. The method comprises the following steps of: additionally arranging an aluminum alloy containing Sc and Zr between two butt-welding plates as filling welding flux; and enabling the high-strength aluminum alloy containing Sc and Zr to be fused into a welding joint structure through stir-friction welding. According to the method disclosed by the invention, properties of the aluminum alloy material are more stable, and a second aluminum alloy material with higher strength is additionally arranged between the two butt-welding plates, so that strength of the welding joint can be improved; and a welding material is reserved in advance, so that a phenomenon that the surfaces of the welding plate are not flat caused by shaft shoulder pressing is eliminated, and therefore, groove defects of the appearance are avoided.