The invention discloses a method for producing ultra-low carbon steel by use of a VD (vacuum degasser) device and belongs to the technical field of refining of molten steel. In the molten steel refining treatment process of the VD device, carbon dioxide is taken as bottom blowing gas for bottom blowing of a steel ladle of the VD device, CO2 and C elements in the molten steel react in the high-vacuum state for forced decarbonization, forced decarbonization and natural forced decarbonization of the molten steel are combined, the decarbonization rate of the VD device is increased, and the metallurgical effect is realized. A steel ladle bottom blowing system is configured with two kinds of gas, namely, carbon dioxide and argon, carbon dioxide and argon can be switched for use, carbon dioxide is used in the vacuum state in the treatment cycle, and argon is adopted in the non-vacuum state in the treatment cycle. The method has the benefits as follows: forced decarbonization and natural forced decarbonization of the molten steel are combined, and ultra-low carbon steel production by the VD device is realized, removal of impurities in steel can be promoted, the desulfurization rate can beincreased, and production of high-purity steel by the VD device is realized; the temperature of the molten steel in the CO2 bottom blowing area is reduced, a bottom blowing brick is protected, and corrosion to the bottom blowing brick is reduced.