The present invention relates to an exhaust gas processing system which simultaneously performs desulfurization and denitrification, and the exhaust gas processing system which simultaneously performs desulfurization and denitrification, according to the present invention, comprises: a cooling part for lowering the temperature of an exhaust gas comprising NOx and SOx; an ozone supply part formed at the rear end of the cooling part, for supplying ozone (O3) to oxidize NOx included in the cooled exhaust gas; and a nozzle formed at the rear end of the ozone supply part, for spraying, in a chamber, an aqueous solution comprising a Ca-based desulfurization agent and KI.