To enhance the static mechanical properties of rivetless joint, a composite process of ultrasonic metal welding and rivetless connection was used. Then, taking 5A06 aluminum and TA1 titanium alloy as the substrates, the connection of Al-Ti dissimilar plates was conducted by rivetless connection, and the ultrasonic welding treatment was performed. Furthermore, the influences of ultrasonic welding on the static mechanical properties of rivetless joints for Al-Ti dissimilar plates were explored by tensile-shear test and microstructure observation. The results show that the ultrasonic welding can improve the forming quality and static mechanical properties of rivetless joint, especially when the aluminum plate is the upper plate. The fundamental mechanism of ultrasonic and rivetless composite process strengthening is the presence of solid-phase welding inside the joint, which leads to the change of stress, from the stress on the neck of joint to the stress on the welded area. Ultrasonic welding improves the plasticity of aluminum alloy plate, while the titanium alloy plate has no obvious change.