A method for recovering iron through copper slag calcination and modification is disclosed. The method includes (1) raising the temperature of a desilicication modifier and copper slag in an inert gasatmosphere to a calcination temperature to free ferrous oxide in fayalite in the copper slag; (2) maintaining the calcination temperature and inert gas protection, communicating the calcination system with outside air, and feeding CO and CO2 at the same time into the roasting system in the step (1) to oxidize the free ferrous oxide into ferric ferrous oxide and enable crystal growth, with the volume percentage of the CO in the total gas components of CO and CO2 being 0-5%; and (3) cooling the product after calcination is finished, performing ore grinding and grading to obtain modified slag with different particle sizes, and performing magnetic separation under a magnetic field to obtain iron ore concentrate and magnetic separation tailings. Iron in the copper slag can be efficiently recovered through industrial waste gas CO and CO2 by the method to obtain the iron ore concentrate suitable for use as an iron melting raw material and the magnetic separation tailings suitable for use asa raw material for building materials such as cement.