Abstract: The crack was prefabricated in different areas of friction stir weld of 2 A12-O aluminum alloy, and the tensile-tensile fatigue crack propagation rate test was carried out. The fatigue crack growth behavior of 2A12-O aluminum alloy friction stir weld in different areas was studied, and the effect of microstructure change on the crack growth rate was analyzed. The results show that the microstructure of friction stir welding area of 2A12-O aluminum alloy changes due to strong mechanical and welding thermal coupling effect of the stir needle, and the microhardness of the weld nugget zone is significantly higher than that of the base material, which is a high-matching weld. When the crack grows steadily, the growth rates of crack prefabricated in the heat-affected zone and weld nugget zone are basically the same, and both are higher than that of the crack prefabricated perpendicular to the weld direction, and there is a significant decline in the growth rate of the crack perpendicular to the weld direction. In the expansion stage, the growth rate of the crack perpendicular to the weld seam direction is gradually higher than that of the crack prefabricated in the heat-affected zone. While, the crack growth rate of the two regions is higher than that of the crack prefabricated in the weld nugget zone.