The invention discloses a method based on laser-CO2 arc hybrid back-gouging-free backing welding, relates to a laser-CO2 hybrid welding technology, and aims to solve the problems that back gouging work is required to be performed and the defects such as incomplete penetration, slag inclusions, air holes and the like appear easily when backing welding is performed on T-shaped joints with K-shaped grooves formed with existing CO2 arc welding technologies under the condition that heat input is not increased. According to the method, laser-CO2 arc hybrid back welding is performed, arcs are locatedin the front to guide laser beams, the arcs and the laser beams act on the same molten bath, under the synergistic effect of laser and the arcs, the molten drop transfer mode is changed, the flowability of the molten bath is increased, flowing of liquid metal towards groove roots, upwards floating of the slag inclusions and escape of gas are facilitated, and the welding joint quality is improved.Besides, according to the method, the back gouging work is omitted, the welding productivity is increased, the environmental pollution is reduced, and the body health of welding persons is protected.