A stereo x-ray inspection apparatus and a method for forming a three-dimensional image through volume reconstruction of an image acquired from the same are disclosed. The apparatus includes one x-ray generator and two detectors to acquire two images. The x-ray generator and detectors are arranged in the form of a right-angled triangle, to easily achieve mathematical development and analysis. One of the detectors, which does not just oppose the x-ray generator, is movable and rotatable, to acquire images under the condition that only one detector is moved in accordance with the size of an object, and thus to simplify control operation for the apparatus, so that a more accurate image from an object moving at high speed is acquired.