Abstract: Using a new method of fillet welding, the friction stir outer fillet welding, we welded the 2519 high-strength aluminum alloy plate 22 mm thick, and analyzed the microstructure and microhardness distribution of fillet welding joint and the reason of the fracture of welding stirring pin, which the type of fracture is shear fracture. The results show that the welding method can effectively carry on fillet welding; the reasonable welding process and welding stirring pin shape are the key of high-quality fillet welding joint. When the rotation speed is 30-40 rad/s and the welding speed is 90-120 mm/min, we can get a high-quality weld appearances.