In recent years, due to the unique physical and chemical effects of ultrasonic waves, it has been widely used in the welding process. High-quality joints were obtained with the ultrasonic vibration was applied during the resistance brazing process. To date, however, little studies have been reported on the microstructure evolution mechanism of joints. In the present study, a Zn-Al alloy was used as filler metal to braze 6063 aluminum alloy using ultrasonic-assisted electrical resistance-brazing technology. The effects of ultrasonic field and electric field on the microstructure evolution of the joints were studied, and its mechanism was also analyzed. The results showed that applying ultrasonic vibration to substrate during brazing process could effectively promote the effective connection between the filler metal and base metal, reduce the defects, improved homogeneity and have obtained the joints with good metallurgical bonding. In addition, both ultrasonic power and electrical current intensity have significant effect on the dissolution during the brazing process. With the increment of ultrasonic power, the dissolution of the base metal was intensified, the Al content in the brazing seam increased, and the eutectoid α-Al phase increased. As the electrical current increases, the primary α-Al phase increases.