Abstract: The weld shape scheme was obtained by FEM for the purpose of improving fatigue strength,the special weld shaping device was developed to keep the weld toe smooth through mechanical impact.The fatigue properties of specimens before and after mechanical shaping were tested by low frequency fatigue testing machine.It is shown that the weld reinforcement became lower and the weld toe radius was increased because of the impact effect on the weld surface by special shaping device.The fatigue life test indicated that the stress concentration on weld toe is reduced and the fatigue strength of aluminium alloy welded joint is improved by the geometric optimization using mechanical shaping method,the fatigue failures of most specimens are initiated on defects of weld and base mental.