The invention belongs to the technical field of steel structure welding and provides a full penetration fillet weld back-gouging-free welding technology. The welding technology comprises the following steps of: 1) processing a groove of a web plate and decreasing the welding groove as much as possible, 2) fabricating a welding body, ensuring an inclination angle of the welding body to allow a center line of a welding wire to be located on a bisector of an included angle between the groove of the web plate and a wing plate during welding, 3) assembling and placing the web plate and the wing plate on the welding body in a push-against manner, ensuring the straightness and planeness of the web plate and the wing plate and accurately controlling focuses of the web plate and the wing plate, 4) selecting an appropriate welding wire material according to performance of a base material, and carrying out carbon dioxide gas shielded welding on a weld on the reverse side of the groove of the web plate to form a welding backing plate for later groove welding, 5) carrying out union melt welding as the first U-shaped groove welding, and 6) carrying out layered filling welding via the union melt welding, and finally carrying out cosmetic welding, wherein the groove of the web plate is a unilateral U-shaped or V-shaped groove.