Abstract: The resistance thermocompression micro-welding process was used to weld the high temperature resistant fine insulated copper wires. The formation process of the joints under various welding voltages, formation of weld, cross-sectional microstructure and breaking force were studied. The results show that when the welding time is 20 ms, the electrode pressure is 12 N, and the welding voltage is greater than 2.05 V, the paint removal and welding of the insulated copper wire can be completed within one output pulse without prior paint removal. Joint width and joint tensile force gradually increase with the increase of welding voltage while the length of the joint remains unchanged. The failure modes of the joints are in turn joint interface separation, joint front section fracture and joint middle fracture. The evolution of the joint consists of five stages: pre-compression plastic deformation, weak bonding joint, thermally assisted indentation, strong bonding joint and melt extrusion.