Abstract: Three different filler metals,Cu foil,Al-Si-Mg foil and Al-Si-Mg/Cu/Al-Si-Mg (ACA) composite foil,were used for vacuum brazing of 45%SiC_p/2024 Al composites. The microstructure of the interface in brazed seams was examined with SEM,EDS and XRD. And the effect of different filler metals on the interfacial microstructure and bonding strength was also analyzed. The formation of interface during vacuum brazing of 45%SiC_p/2024 Al composites with different filler metals and the fracture mechanism of the joint were revealed. The results indicate that ACA composite filler metal,combining the advantages of both Cu foil and AlSiMg foil,had lower liquidus temperature and better flowability. Through the diffusion of Cu atoms and prior eutectic reaction at the interface between aluminum alloy substrate and its oxide film,the removal ability of oxide film of the filler metal was enhanced and joining of 45%SiC_p/Al composites was achieved with high quality.