A CT system for security check and a method thereof are provided. The method includes: reading inspection data of an inspected object; inserting at least one three-dimensional (3D) Fictional Threat Image (FTI) into a 3D inspection image of the inspected object, which is obtained from the inspection data; receiving a selection of at least one region in the 3D inspection image including the 3D FTI or at least one region in a two-dimensional (2D) inspection image including a 2D FTI corresponding to the 3D FTI, wherein the 2D inspection image is obtained from the 3D inspection image or is obtained from the inspection data; and providing a feedback of the 3D inspection image including at least one 3D FTI in response to the selection. With the above solution, it is convenient for a user to rapidly mark a suspected object in the CT image, and provides a feedback of whether a FTI is included.