The in-situ synthesis of AlMgB14-TiB2 composite and its simultaneous diffusion bonding to Nb and Mo were achieved by FAPAS sintering process. XRD, SEM and EDS were used to analyze the phase composition, microstructure and elements distribution characteristics in the joint interface; the formation mechanism of diffusion layer and the process of diffusion bonding under multi-physics coupling condition (electric field, temperature field and pressure field) were discussed. Results indicate that the simultaneous synthesis and diffusion bonding of AlMgB14-30 wt%TiB2 composites to Nb and Mo could be realized, forming uniform and dense diffusion layers with an average width of about 170~180 μm; TiB2 particles gather in the joint interface during the sintering process and react with the metal to form intermetallic compounds; the continuous diffusion of boron element driven by concentration gradient and the formation of intermetallic compounds are the main mechanisms in diffusion bonding.