Abstract: The surface of T2 violet copper terminals was ground with sandpaper to obtain different surface roughness （1.80, 1.15, 0.62, 0.36, 0.14 μm）. The EVR25 mm² copper wires and violet copper terminals were welded by ultrasonic welding. The influence of terminal surface roughness on the forming quality and tensile properties of the joint was studied. The results show that as the surface roughness of the terminals decreased from 1.80 μm to 0.14 μm, the porosity of the joints decreased from 11.76% to 8.15%. With decreasing surface roughness of the terminals, the porosity between copper silks and at the copper wire/terminal interface decreased, the bonding between interface became tighter, and the combination form changed from point connection and line connection to line connection and surface connection; the forming quality of the joint improved. With decreasing the surface roughness of the terminals, the average peak load of the joint during the tension increased, the adhesion degree of copper wire on the terminal intensified, and the failure form of the joint changed from mainly interface pull-off to mainly large-scale adhesion of copper wire.