Traditional industrial computed tomography systems generally calibrate the central ray by scanning a wire phantom. That is time-consuming and slow. This paper presents a direct central-ray determination method using the projection data of the object to be examined. The basic idea is that with a fan-beam arrangement, any straight line on the object slice will align with the x-ray point source at only two times during a 360-deg scan. By measuring the mismatching of the two sets of projection data that correspond to these two alignments, the true central ray can be identified at the minimum of the measurement. Our test has proven that this automated method is fast, reliable, and accurate.