Abstract: To address the issue of welding defects in laser welding of copper wire conductors, which are caused by high reflectivity and high thermal conductivity, filler materials were introduced to avoid defects and enhance tensile strength. Comparing the tensile strengths of three processes, namely non-filler autogenous welding, pure Ni powder filling, and CuCrZr powder filling. It was found that the joint with pure Ni powder filling exhibited the highest tensile strength of 282 MPa, representing increases of 16.3% and 11.7% compared to 242.5 MPa for CuCrZr powder filling and 252.5 MPa for autogenous welding, respectively. To explore the causes of tensile strength differences, further microstructural characterization and microhardness testing were conducted. The results show that, compared with laser welding using CuCrZr powder as filler material or without filler material, the welding joint with pure Ni powder as filler material had fewer defects. Additionally, Cu_3.8Ni and Cu_0.81Ni_0.19 phases conducive to strength improvement were formed at the welding interface. The average grain size at the nugget/heat-affected zone interface of the pure Ni powder filler and autogenous welding was approximately 29 μm, showing little difference, which was significantly smaller than 46.84 μm for CuCrZr powder filler. Moreover, the pure Ni powder filler exhibited more uniform texture distribution and the highest proportion of high-angle grain boundaries, which contributed to enhancing the interface strength. The average microhardness of the welding joint with pure Ni powder filler reached 209 HV, far higher than 51.8 HV for CuCrZr powder filler and 56.1 HV for autogenous welding.