Abstract: The present disclosure discloses a welding gas shielding device, a laser filler wire welding system and a welding method. The welding gas shielding device comprises an upper shielding gas dragging cover device and a back shielding gas device. The laser filler wire welding system comprises a welding gas shielding device, a height adjusting mechanism, a wire feeding system, a laser system, a numerical control console and the like. The welding gas shielding device for narrow gaps made of dissimilar materials is reasonable in structural design, gas shielding can be carried out on the upper area and the lower area of a welding area in the welding process of the narrow gaps made of dissimilar materials, the problem that laser narrow-gap welding gas shielding is insufficient and unstable is solved, the weld joint cooling speed can be adjusted and controlled, the shielding effect is enhanced, and the welding efficiency is improved.