Abstract: The present invention belongs to the technical field of metallurgical solid waste resource utilization, and particularly relates to acidification and carbonization coupling modified steel slag as well as a preparation process and an application thereof. The process specifically includes the following steps of adopting acetic acid, tributyl phosphate, ethanolamine and a NaOH and Ca(OH)2 emulsion as reaction reinforcing agents, and modifying the steel slag together with CO2-rich lime kiln flue gas. The process for modifying the steel slag through acidification and carbonization coupling provided in the present invention has the advantages of simple reaction conditions and no need of high-pressure CO2, additionally, the carbonation reaction rate can be greatly increased, and f-CaO and f-MgO in the steel slag can be effectively eliminated.