To improve the overlap welding strength and metallurgical compatibility of copper/steel transition joints, a dissimilar metal microtexture-melting laser overlap welding method was proposed. First, ultrafast green laser was used to prepare microtextures on the surface of the steel substrate to improve the wettability and occlusion strength of the steel side interface during the overlap welding, and then copper/steel fusion overlap welding was performed on different microtextured surfaces by pulsed green laser. The microtexture morphology, joint microstructure, bonding interface, tensile properties and fracture mechanisms were studied. The results show that the higher laser power and etching times, the greater the degree of thermal ablation, which easily leads to the deterioration of the internal quality of the groove. The surface texturization has a significant effect on the joint microstructure and tensile strength, and surface texturization can strengthen convective mass transfer, enhance the diffusion of copper to the bottom of the molten pool (steel side), and help the formation of α-Fe and γ-Fe solid solutions with higher copper content, which makes the microhardness of the bottom of the molten pool higher. When the groove depth is 89.91 μm, the tensile strength of the textured joint is the largest, which is 112.5 MPa, 19.5% higher than that of the untextured joint. The fracture mechanism of joints is ductile fracture. The improvement of tensile properties is due to solid solution strengthening, the increase of fusion volume and the vortex bite.