n this paper,the effects of high cycle alternating stress loading on mechanical properties and microstructures of overlap joints of 6005 A aluminium alloy profile by MIG welding with pre-accelerated test were studied. The results show that the average tensile strength of the specimens without accelerated test is 204.836 3 MPa. The average tensile strength of the specimens with 60% fatigue limit accelerated test is 204.028 2 MPa and the fracture location is HAZ. The average tensile strength of the specimens with 90% fatigue limit accelerated test is 188.701 6 MPa;and the weld of the specimens without accelerated fatigue limit accelerated test is 188.701 6 Ma. The average hardness of the core is 69.30 HV,the average hardness of the weld center of 60% accelerated fatigue specimens is70.07 HV,and the average hardness of the weld center of 90% fatigue specimens is 66.45 HV. The average impact energy of the samples without accelerated test and 60% fatigue limit accelerated test is 6.67 J,and that of the samples with 90% fatigue limit accelerated test is 6 J. The reason for the change of properties lies in the change of grain size and morphology. When the load is higher in accelerated test,the grain of welded joint is elongated,resulting in coalescence,the decrease of grain boundary area and the decrease of grain boundary energy storage.