Abstract: The welding joint and repair welding joint of A7N01 aluminium alloy are analyzed in this paper,the mechanical properties of the welding joint before and after repair welding were studied by welding residual stress measurement,tensile test,micro-hardness test,metallographic observation and fracture toughness test,respectively. Based on the fracture toughness theory,the critical crack length of the structure before and after repair welding is calculated. With the initial crack length determined by metallographic observation,the residual fatigue life before and after repair welding is calculated using Paris for-mula. The result shows that although the repair welding degrade the welding joint property to some extent,it is still an efficient method to make sure the structure with flaw has enough load-carrying capacity.