Abstract: Al-Si-Cu alloy powders were used as insert layers for diffusion brazing of aluminum/copper dissimilar metals. The microstructure of resulted Al/Cu joints was observed by SEM,EDS and XRD. The mechanism of joint formation was analyzed with ternary phase diagrams. The mechanical properties of the joints were tested. The results show that uniform and compact joints were obtained at 530℃ for 60 min under the applied pressure of 1 MPa. A large number of eutectic phases existed in the joint. The interfaces on both sides were different. Cu₃Al₂,CuAl and CuAl₂ formed near the interface on copper substrate side, but a diffusion area without IMC existed near the interface on aluminum substrate side. The shear strength of the joints changed with the holding time. The maximum shear strength of the joint brazed at 530℃ for 60 min reached 35 MPa.