Abstract: The fatigue tests of bobbin tool friction stir welding profile joints of 3.3 mm thick 6005A-T6 aluminum alloy with different dimensions were carried out to analyze the fatigue performance of the joints. Combined with the macroscopic forming and microstructure evolution of the joint under typical parameters, the fracture behavior of the bobbin tool friction stir welded joint was revealed. The results showed that the tensile fracture of the joint under typical parameters (rotation speed of 1 000 r/min, welding speed of 100 mm/min, width and thickness of parallel section of 11.8 mm and 3.1 mm) was located in the HAZ-RS. The grain structure characteristics in the TMAZ-AS of the joint could influence the fatigue cracks generation and propagation. The SEM analysis of fatigue fracture showed that no obvious defects were found. The fatigue cracks propagation and fracture zones showed typical fatigue fracture characteristics, and the fracture was located in the TMAZ-AS of the joint