The invention provides a welding method for Q420qENH coating-free weathering steel for a steel bridge. According to the Q420qENH coating-free weathering steel, the atmosphere corrosion resistance index I is larger than or equal to 6.5, and the welding sensitive index Pcm is smaller than or equal to 0.23. When the welding joint manner of the Q420qENH coating-free weathering steel is the butt weld, the solid wire gas shielded welding bottoming and union melt welding cover face filling combined welding process is adopted; when the welding joint manner is the T-type fusion penetration fillet weld, the flux-cored wire gas shielded welding process is adopted; and when the welding joint manner is the deck slab single-sided welding double-sided forming joint weld, the solid welding wire gas shielded welding bottoming and union melt welding cover face filling combined welding process is adopted. According to a welding wire, the atmosphere corrosion resistance index I is larger than or equal to 6.5, the fused metal relative corrosion rate is smaller than or equal to 8%, the matching of the weld and ingredients of a steel plate is guaranteed, the problem about the weather resistance of the weld of the coating-free weathering steel is solved, and the technical difficulties of application and popularization of the coating-free weathering steel are solved.