In order to investigate the effect of ultrasonic assistance on the microstructure and properties of 2219 aluminum alloy welded joint, the butt welding test on 3 mm thickness 2219-T87 aluminum alloy plate was carried out by ultrasonic assisted friction stir welding method. The microstructure, mechanical properties, three?dimensional deformation measurement, fracture scanning and XRD were studied. The results showed that the tensile strength was increased by 8.48% and the fracture strain was raised by 9.25% owing to the addition of high frequency ultrasonic vibration to the friction stir welding technology. At the same time, it also effectively improved the upper and lower inhomogeneity of the microstructure of the welded joint, and increased the size of weld bottom cross sections. Particularly, the formation of the defects was inhibited at the bottom of the weld, which can improve the overall strength of the weld. Through the XRD test, it was confirmed that with the decrease of welding temperature, the degree of dissolution of the main strengthening phase θ ″ and θ ′was reduced, and the coarse θ phase particles’s aggregation extent reduced after the addition of ultrasound to the friction stir welding, which improved the mechanical properties greatly.