disclosed is an exhaust gas treating system having an exhaust gas treating apparatus for carbon dioxide capture process which additionally removes harmful substances remaining in the gas discharged from the existing flue - gas desulfurization process by using separation membrane so as to efficiently carry out the carbon dioxide capture process . the exhaust gas treating system using polymer membrane , comprises a carbon dioxide capture equipment for capturing carbon dioxide from the exhaust gas of a boiler , a flue - gas denitrification equipment placed between the boiler and the carbon dioxide capture equipment , a dust - collecting equipment and a flue - gas desulfurization equipment .