Strengthening and toughening welds are the keys to improving the mechanical properties of high-performance bridge steel welds. Optimizing weld performance through microstructure control is an effective way to achieve this goal. Taking 500 MPa high-performance bridge steel as the research object, the typical characteristics of its weld microstructure were systematically analysed, and a mapping relationship between microstructure and impact toughness was established, providing a theoretical basis for the strengthening and toughening design of high-performance bridge steel welds. Research has shown that the small and staggered distribution of needle-like ferrite forms a "basketweave", which increases the energy required for crack initiation and propagation and improves the impact toughness of welded joints. The polygonal ferrite structure is prone to intergranular cracks due to the large difference in grain boundary orientation, which reduces the crack initiation energy of welded joints. The hindering effect of the coarse needle-like ferrite structure on crack propagation is significantly reduced, resulting in a decrease in the impact toughness of the welded joints.