Abstract: When combined with the high-temperature reaction characteristics of carbon dioxide—that is, the weak oxidation, endothermic, or weak exothermic effect compared with oxygen and the bubble increment effect of reacting with carbon to produce twice the gas—the carbon dioxide smelting process was targeted according to the different tasks in different periods of converter smelting. Before temperature measurement, sampling, and carbon determination using the sublance system, carbon dioxide is blown into the converter from the upper oxygen gun and the bottom blowing element of the converter. By changing the ratio of carbon dioxide and oxygen in the oxygen gun, an industrial experimental study was conducted on the effect of the carbon dioxide ratio blown from the upper oxygen gun on the endpoint of the mass fraction of phosphorus and nitrogen and the carbon–oxygen concentration product. The results show that with the gradual increase of the carbon dioxide top blowing ratio from 4.84% to 9.68% in the early and middle stages of converter smelting, the mass fraction of phosphorus at the end of the converter first decreases and then basically remains unchanged. The mass fraction of nitrogen also decreases gradually, but the decreasing range becomes smaller, and the changing trend of carbon–oxygen concentration product is the same as that of TFe in slag, which first decreases and then increases. The optimal carbon dioxide top-blowing ratio varies with the index. Furthermore, the test also shows that even if all the blown carbon dioxide reacts to generate additional carbon monoxide gas and the nitrogen is removed by the additional carbon monoxide gas generated compared with the original process, the partial pressure of nitrogen in the additional gas is much higher than the partial pressure in equilibrium with the mass fraction of nitrogen in the liquid steel. This indicates that the improvement of the denitrification effect is due to the additional gas generated by the reaction of blowing in carbon dioxide; it improves the denitrification effect of the original gas, and the generation of additional gas improves the kinetic conditions of the molten pool and facilitates the mass transfer of nitrogen. The highest decreasing ratio of the endpoint mass fraction of phosphorus, nitrogen, carbon–oxygen concentration product, and TFe in the slag of the test converter was 20.4%, 34.3%, 12.92%, and 8.89%, respectively.