An X-CT scan system includes a base, an object rotary support, an X-ray generation device and a data acquisition system, wherein one side of the detector is leveled to or beyond the prolong line of the connecting line between the X-ray source of the X-ray generation device and the center of the object rotary support, the length of the beyond portion is less than the radius of the imaging field. The advantage of the invention is in that the invention can reconstruct the entire image of the object by means of X-ray projection data which only covers half of the area of the object. Compared with the traditional CT scan system, half of the detector size can be saved at most. The X-CT scan system is simplified and the projection data amount for scan and computation amount for image reconstruction are also reduced with the reconstructed image quality guaranteed.