Abstract: In view of the connection problem of high-power well heating cable materials in long horizontal wells during heavy oil field exploitation, laser-arc composite welding technology was adopted to realize the welding of copper-nickel alloy and T2 copper dissimilar metals by filling pure nickel welding wire. The microstructure and mechanical properties of the welded joint were analyzed. The results show that the welded joint with good shape, no porosity and no unfused welding defects can be obtained by using laser-arc composite filling wire welding. The microstructure of T2 copper side and copper-nickel alloy side are dominated by massive equiaxed crystals, and the weld area is dominated by columnar crystals. The diffusion rate of copper atom to the fusion zone is greater than that of nickel atom to the copper base material side, and the intermetallic compound is not formed between the two elements. The tensile fracture of the sample occurs on the copper base material side, indicating that the strength of the joint is higher than that of the copper base material. The solid solution strengthening phenomenon in the welded joint area leads to the trend of hardness from copper-nickel alloy to copper side increasing first and then decreasing.