Copper has extremely high thermal conductivity and laser reflectivity. Hence, incomplete fusion and undercut problems commonly occur on the copper side during the laser welding of copper and steel. Herein, the laser welding process of T2 copper and SUS304 austenitic stainless steel was performed under two laser deflection angles using the 4-kW fiber laser. The deflection of the laser beam on the steel side can significantly increase the amount of copper in the weld, suppress weld forming defections, promote the mixing of the weld microstructure, optimize the connection form of the weld joint, and promote the smooth transition of components at the copper side interface. Consequently, reliable weld joints can be obtained.