Abstract: The joining of dissimilar metals can achieve complementary advantages of different metal materials and is widely applied in fields such as electric vehicles, electronic power systems, and aerospace. However, achieving reliable welding of dissimilar metals remains highly challenging. Ultrasonic welding technology, with its advantages of low heat input, no melting, and high efficiency and environmental friendliness, has become a research hotspot for welding dissimilar metals such as Cu/Al, Fe/Al, and Mg/Al. The current research status of ultrasonic welding of Cu/Al, Fe/Al, and Mg/Al was reviewed from three perspectives: plastic flow at the welding interface, growth of intermetallic compounds, and grain morphology. The atomic diffusion mechanism at the interface of dissimilar metals in ultrasonic welding was analyzed, the effects of interlayers and auxiliary energy fields on the microstructure and mechanical properties of ultrasonic welded joints of dissimilar metals were summarized, the relationship between process, formation, microstructure, and mechanical properties was discussed, and the development trend of microstructure control technology in ultrasonic welding of dissimilar metals was prospected to provide a reference for the research direction of ultrasonic welding of dissimilar metals.