A method of reducing an artifact by using structural similarity. The method includes at least: obtaining a plurality of input Computed Tomography (CT) images including a first CT image and a second CT image, generating an artifact map in which anatomical information is removed and artifacts information is remained, by subtracting the second. CT image from the first CT image, generating, by the computer, a structural similarity map between each CT image and the artifact map, and generating, by the computer, a final reconstructed image by comparing particular parts on images of a plurality of structural similarity maps with each other and selecting data of an input CT image which has been used to generate a particular part of a structural similarity map having a lowest degree of structural similarity, as data of a particular part on the final reconstructed image.