Abstract: The computational method of deformation of T joint of aluminum-Li alloy with thickness of 2.5 mm welded by double beam laser was studied.By taking account of the change of mechanical characteristics of the weld metal in heating,melting, cooling and solidifying process,and the forming process of the T joint,a method of calculating the deformation of T joint welded by double beam laser welding was developed based on birth-death control by the temperature of each element.In the method,an element was killed or activated according to its temperature during welding.The welding deformation obtained by two different computational methods were compared,one using the birth-death control method,and the other not.Except the above difference,material,geometry,boundary and initial conditions were identical for the two computational methods.The results showed that,whether using the birth-death control or not, which had an important influence on the computational results of deformation of T joint welded by double beam laser welding,and the reason was analyzed.