Abstract: Objective Welding of titanium/steel dissimilar materials has significant engineering application value in fields such as aerospace, petrochemical industries, and marine engineering. However, due to physical property differences between titanium and steel, performance of welded joints is severely deteriorated. In response to challenges such as difficulties in welding titanium/steel dissimilar material during production process, Ni-containing welding wires are employed to address these issues and enhance welding quality. Methods Dissimilar materials of TC4 titanium alloy and Q235 steel were welded by gas shielded metal arc welding method and Cu-Ni welding wires with different Ni contents, and effect of different Ni contents in welding wires on microstructure and mechanical properties of welded joints was studied in this paper. Results The test results show that high Ni content in welding wire leads to instability of welding process, which reduces performance of welded joints. Ni content also has a great influence on microstructure of weld. When Ni content is low, Ni-rich dendrites and Cu-rich dendrites are formed on both sides of weld of TC4 titanium alloy and Q235 steel respectively. Due to Fe and Ti elements diffusion of base metal on both sides of fusion line, while combining with Ni and Cu elements, an obvious welding interface layer is formed. With the increase of Ni content in welding wire, microstructure of weld changes from dendrite to microstructure formed by the combination of Ni-rich cellular structure and Cu-rich network structure, and hardness of weld increases. Conclusion Research shows that Ni can enhance weld strength. However, excessive Ni content causes instability of welding process. Therefore, employing CuNi10 welding wire results in satisfactory dissimilar material welded joints between titanium and steel.