In order to solve the problem of weakening of Al–Li alloy after laser beam welding (LBW) which is applied to a type of civil aircraft fuselage panel, three post–processing methods which were shot peening and heat–treatment + peening were studied. The tensile test, fatigue test and residual stress test were carried out to evaluate and reveal the strengthened effect and mechanism. The results show that fatigue performance is improved significantly but tensile property is reversed. The DFR_cutoff values of 0.20mmN and 0.36mmN shot peening are increased by 27.8% and 118.5% compared to original welding state. Better overall performance is presented by heat–treatment of solution and aging + shot penning, which the tensile strength is increased by 32% and the DFR value is increased by 21.9% compared to initial state.