An X-ray image processing method, including obtaining a first X-ray image of an object including a plurality of materials including a first material and a second material different from the first material; obtaining three-dimensional (3D) information about the object using a 3D camera; obtaining first information about a thickness of the object based on the 3D information; and obtaining second information related to a stereoscopic structure of the first material by decomposing the first material from the object using the first information and the first X-ray image.