Abstract: For 5.4 mm thickness 2219 aluminum alloy,floating bobbin friction stir welding test and engineering application research were carried out. Welding parameters of low rotation speed and high welding speed were used to obtain welded joints with well formation and excellent performance. Both ultrasonic phased array inspection and X-ray inspection of welds met the requirements of first-class welds in the standards of the aerospace industry. The average tensile strength of the joint reached more than 70% performance of the base metal,and the elongation rate reached more than 6.5%. The welded joints were all 45° shear ductile fracture and had good plasticity. The weld section was wide at the top and bottom,narrow in the middle. The thermo-mechanically affected zone on both sides of the weld had a parabolic shape,and there was no weld nugget protrusion. Based on a large number of tests and verifications,it was the first to realize the engineering application of this technology in the welding of rocket tanks. Welding of the shell section in a certain type rocket fuel tank was successfully completed,and the weld successfully passed the normal temperature hydraulic pressure test and liquid nitrogen cryogenic test assessment.