Abstract: The cold drawing process of large drawing, medium drawing, small drawing and fine drawing was used to prepare ultra-fine copper wires for cables, and the ultra-fine copper wires were annealed. The microstructure and mechanical properties of the ultra-fine copper wires were studied. The results show that ultra-fine copper wires with a diameter of 0.05mm can be successfully prepared with the oxygen-free copper bar with a diameter of 8.0 mm. After annealing heat treatment,the mixed microstructure of ultra-fine grains and coarse grains is formed inside the ultra-fine copper wires, and the grain size is continuously distributed from 0.6 μm to 13.8 μm, forming a typical "multi-modal" grain structure. During tensile deformation,the heterogeneous interface can be formed at the interface between the ultra-fine grains and the coarse grains. In addition,geometric necessary dislocations form at the heterogeneous interface, leading to synchronous improvement of strengthening effect and hardening ability of the ultra-fine copper wire. Consequently, the ultra-fine copper wire with good matching between strength and elongation is achieved with ultimate tensile strength of 280.1 MPa and elongation at break of 12.8%.