Target area localization or radiotherapy localization is often done in two ways: conventional simulator localization and, most commonly, CT simulator localization in the context of precise radiotherapy. Conventional simulator positioning mainly uses the principle of X-ray fluoroscopic imaging to capture the relationship between the projection of the target area in the direction of the irradiation field that endangers the organ and other surrounding normal tissues, and then involves the irradiation field direction, size and shape according to the relationship between the projection position and the reference mark on the body surface. However, nowadays, the conditions of precision medicine are using CT simulation for positioning, which has the following main steps: 1. Determine the patient’s treatment position; 2. Often use body surface fixation devices, such as heat shrinkable film and vacuum pads to fix the patient’s position, especially for thoracic tumors can limit the change of tumor position caused by respiratory dynamics to a certain extent; 3. Select the appropriate conditions for tomography, that is, CT scan; 4, Use the software of virtual simulation to reconstruct the 3D image of the patient, determine the isocenter position, determine the isocenter position according to the position of the bed and the position of the laser point, and mark the marker point on the membrane or skin; 5. Finally, the scan image and the isocenter position are transmitted to the planning system of radiotherapy department through the simulated information system, and the patient can get down from the CT simulator after doing this, and the whole positioning process is finished.