The input-output model of carbon flow at the process level and pre-iron system level is constructed based on the analysis on carbon flow and energy flow in the pre-iron system and the principle of carbon balance; it is concluded that the carbon emission potential of gas combustion in the coking process, solid fuel and ignition gas consumption in the sintering process, coke and coal injection consumption in the iron-making process is the greatest, while it is also pointed out that changing the energy structure of the pre-iron system and paying attention to the recovery and low carbon utilization of blast furnace gas and coke oven gas as well as developing new energy-saving technologies are important measures to solve the problem of CO₂ emissions in the pre-iron system.