Abstract: In this study,a specially designed rivet with double flange structure was used to fabricate ultrasonic welding-riveting hybrid joints of30% carbon fiber reinforced PA6 composite materials. The macro appearance,cross-section,failure mode,shear strength and peel strength of hybrid joints were investigated,and improvement mechanism of mechanical properties of hybrid joints was analyzed. The results showed that the hybrid joining process of ultrasonic welding-riveting consisted of five stages,coulomb friction phase,upper workpieces riveting phase,lower workpieces riveting phase,melting phase and solidification phase of materials on the faying surface. The double-flange rivets avoided the formation of flash in riveting site,resulted in the excellent mechanical interlocked of flanges of the rivets with the workpieces and the formation of the weld around the rivets. Therefore,the shear strength,peel strength and energy absorption ability of hybrid joints were improved. Compared with shear strength,ultrasonic welding-riveting process improved the peel strength more significantly. Compared with the ultrasonic welded joints,the ultrasonic welded-riveted hybrid joints that were produced with optimum parameters increased the shear strength,peel strength by29. 9% and 39. 2%,respectively. The improvement of shear strength and peel strength of the hybrid joints attributed to the combination effect of the mechanical interlock of the rivet flange with the workpieces and the weld around the rivets.