Abstract: In view of the difficulties and adverse effects of high reflectivity of copper on laser welding, a copper laser welding method based on stepwise gas medium is proposed. The surface of copper was blackened, the oxide film was formed on the surface of the welded parts, the roughness of the material surface was changed, the laser energy was repeatedly absorbed, and the absorption rate of the laser welding of copper was improved. The final weld formation, macro-morphology, depth of fusion, weld width and mechanical property under different oxygen flow rates were compared, and the mechanism of the method was explored. The results show that when Q ≤ 8 L/min, the penetration and width increase with the increase of oxygen flow rate. When Q = 8 L/min, the copper sheet is fully welded and weld is well formed. The main component of the blackened layer is copper oxide, the overall thickness of the blackened layer in the weld zone is 470 μm, and the blackening degree gradually decreases along direction of the base metal from the weld center. The microstructure of the weld and the heat-affected zone is composed of non-directional α solid solution, and the sides of the weld center are columnar crystals grown along the horizontal direction. Compared with conventional welding, the hardness of weld center is significantly improved and the tensile strength is well, which proves that the stepwise gas protection method can effectively improve the absorption of laser energy of copper and will not cause the mechanical properties of copper laser welded joints to decline under the condition of stepwise gas medium.