Abstract: A connection method is designed to connect AlN ceramic and Cu at low-temperature while used in high-temperature environment in high-temperature power devices. The Sn-Al-Cu active solder layer was plated on the surface of AlN by ultrasonic-assisted fusion welding in the atmospheric environment of 350 ℃, and then the AlN ceramic and Cu were TLP-connected at holding temperature 300 ℃. The microstructure and phase structure were analyzed by scanning electron microscope, energy spectrometer and transmission electron microscope. The mechanical properties of the samples were tested by universal mechanical testing machine. The results show that the active solder and AlN ceramic have achieved good bonding when the plating time is 180 s. A layer of Al adsorbed on the surface of AlN ceramic under the action of ultrasound is observed to be oxidized at the AlN ceramic/active solder interface, and the amorphous Al₂O₃ layer with a thickness of about 20 nm is formed under large undercooling degree. When the holding time is 60 min, all the Sn in the weld is transformed into Cu₃Sn and Cu₆Sn₅; when the holding time is 240 min, the interconnected joints in which all the welds are composed of Cu₃Sn are formed. The shear strength of AlN ceramic/Cu decreases with the prolongation of holding time. The shear strength of the all-Cu₃Sn joint is about 31 MPa. The fracture occurs at the Cu₃Sn/AlN interface, forming an all-intermetallic AlN ceramic/Cu interconnection joint.