Top gas recycling is considered as one of the highest potential technologies to improve reduction efficiency and correspondingly to reduce carbon consumption. As a typical nitrogen free ironmaking process, pre-reduction shaft furnace of COREX^® process (COREX^® shaft furnace) for short is suitable to adopt the technology aiming to cut down CO₂ emission. Under the premise of constant total injection volume, three kinds of reducing gas injection methods are numerically studied by employing a two-dimensional mathematical model. The method that 20% of total reducing gas in volume fraction is blasted through normal inlet (NI) while the rest through down pipe inlet (PI) rather than deadman inlet (DI) could apparently improve gas flow in the inactive zone located near the bottom direct reduced iron (DRI) outlet, thus increasing DRI reduction degree to 61% under present calculation conditions. Meanwhile, either decreasing the vertical height of PI or increasing its diameter makes further improvement on furnace efficiency. After adopting top gas recycling to the shaft furnace by NI+PI method with optimal parameters, CO utilization ratio reaches above 46% when DRI reduction degree correspondingly increases by 12%, what's more, CO₂ emission from the whole process is reduced by about 540 Nm³/tHM. The results prove that top gas recycling technology promotes reduction efficiency inside shaft furnace and greatly reduces the greenhouse gas emission, which will contribute to suppressing global warming.