The experiments of ultrasonic welding were carried out for BVR2.0 copper (Cu) cables and BLV6.0 aluminum (Al) cables with different welding parameters. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), temperature measurement, microhardness evaluation and tensile tests were conducted to investigate the microstructure and mechanical properties of Cu-Al cables joints. The results show that the tensile load of Cu-Al joints reaches 355.6 N, while the welding parameters are set as follows: welding pressure of 0.21 MPa, amplitude of 31%, and time of 860 ms. The diffusion thickness of well-welded Cu-Al joint is only about 3 μm and the peak temperature is 212 °C, which avoids the formation of intermetallic (IMC) effectively. The joint fractures on the copper side rather than the interface of the Cu-Al with a ductile-brittle hybrid fracture mode, indicating that the joint has excellent properties.