Abstract: The characters and mechanism of submicron aluminium matrix composite (Al₂O_3p/6061Al) welding, by use of direct diffusion welding and interlayer diffusion welding, have been investigated, and the effect of interlayer on joint strength has been analysized. The result showed that there existed a critical temperature region between liquid and solid temperature of aluminium matrix composite. When diffusion welding happened in this temperature region, through the soakage of liquid base metal, reinforcement-reinforcement contact in diffusion joint surface converts to the organic integrating of reinforcement-base-reinforcement, and high quality welded joint were obtained. More research shows that, by using proper base interlayer, reinforcement-reinforcement contact in diffusion joint surface can convert to the organic integrating of reinforcementbase-reinforcement toe. Augment of scope of critical temperature region can make joint performance more stabilized and joint distortion more reduced (<2%).