Ultrasound-promoted transient liquid phase bonding (U-TLP) is a high quality, high efficiency, and low-cost method for fast bonding of difficult-wetting materials in the atmospheric environment. In this paper, U-TLP was used to bond SiC particles reinforced aluminium-based metal matrix composite which particle volume fraction was 70%. The pure zinc foil was used as the intermediate layer. The effects of ultrasonic on microstructure evolution and mechanical properties of joints during the transient liquefaction stage were investigated. The mechanism of ultrasonic effects in the transient liquefaction stage of U-TLP was also inducted. The results showed that high volume fraction SiCp/Al MMCs were bonded well at low temperature in the air environment. Ultrasonic vibration can remove the oxide film on the surface of aluminum matrix composites, enhance the wettability of SiC particles with weld metal, promote atomic diffusion and homogenization of SiC particles, and improve the welding quality and efficiency. Reasonable increase of ultrasonic vibration time could effectively improve the joint strength.