Reducing CO emissions of the iron and steel industry, a typical heavy CO-emitting sector, is the only way that must be passed to achieve the 'dual-carbon' goal, especially in China. In previous studies, however, it is still unknown what is the difference between blast furnace-basic oxygen furnace (BF-BOF), scrap-electric furnace (scrap-EF) and hydrogen metallurgy process. The quantitative research on the key factors affecting CO emissions is insufficient. There is also a lack of research on the prediction of CO emissions by adjusting industrial structure. Based on material flow analysis, this study establishes carbon flow diagrams of three processes, and then analyze the key factors affecting CO emissions. CO emissions of the iron and steel industry in the future is predicted by adjusting industrial structure. The results show that: (1) The CO emissions of BF-BOF, scrap-EF and hydrogen metallurgy process in a site are 1417.26, 542.93 and 1166.52 kg, respectively. (2) By increasing pellet ratio in blast furnace, scrap ratio in electric furnace, etc., can effectively reduce CO emissions. (3) Reducing the crude steel output is the most effective CO reduction measure. There is still 5.15 × 10-6.17 × 10 tons of CO that needs to be reduced by additional measures.