Disclosed herein are an X-ray imaging apparatus and an X-ray image generating method in which constituent materials of a target object are separated and mapped to different colors in order to provide one image which has improved distinction between tissues. The X-ray imaging apparatus includes an X-ray generator which generates X-rays and irradiates the X-rays toward a target object, an X-ray detector which acquires X-ray data which corresponds to a plurality of energy bands by detecting X-rays which have passed through the target object, and a controller which acquires a plurality of material images in which a plurality of materials constituting the target object are respectively displayed and brightness information from the X-ray data, generates one image by mapping different color channels to the plurality of material images and combining the plurality material images into a single image, and applying the brightness information to the generated image.