Abstract: The cause of weakeness of Al-Li alloy 2091 joint has been analyzed. And the effectof post-weld heat,treatment on strength of alloy 2091 welded joint is investigated. A newmethod, double stages solid solution and artifitial ageing treatment is present to strength.en Al-Li alloy welded joint. The result shows that this method can increase not only thetensile strength but also the ductility of the alloy 2091 welded joint.