The work aims to optimize the comprehensive performance of electroless copper-plated aluminum nitride (AlN) substrate, master the effect of heat treatment on its coating density, interfacial bonding strength and thermal conductivity, and analyze the failure of scratching layer. The surface of AlN substrate was metallized by electroless copper plating and treated thermally at 300~500 ℃. The phase, microstructure and thermal properties of the Cu-AlN substrate were analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM) and laser thermal conductivity measurement. The adhesion of the coating was investigated by the scratch method, and the failure behavior of the coating was analyzed by the scratch morphology. The surface of the Cu-AlN substrate not treated thermally was bubbling with a bonding strength of 24.7 N and a thermal conductivity of 156.8 W/(m?K). The heat treatment eliminated the bubbling phenomenon of the Cu-AlN substrate. The Cu-AlN substrate treated thermally at 300 ℃ had excellent comprehensive properties with uniform distribution of Cu particles on the surface. The microstructure was relatively compacted with 32.6 N bonding strength and 163.8 W/(m?K) thermal conductivity. The surface of the Cu-AlN substrate treated thermally at 500 ℃ was oxidized to form CuO, and the bonding strength was sharply reduced to 18.5 N with 161.2 W/(m?K) thermal conductivity. The failure mode of Cu-AlN substrate was point peeling. With increasing scratch loading, the point peeling increased, the Cu coating cracked and the AlN base layer appeared to gradually expose. The macroscopic failure of Cu coating exhibited plough trenches caused by plastic deformation. The core of the wear profile was stretched and the boundary was crimped. The reasonable heat treatment of Cu-AlN can optimize its surface microstructure and density of the coating, resulting in the improvement of the bonding strength and thermal conductivity.