The present invention provides a CT image calibration method and device and a CT system. The method includes: arranging a fixed calibration element at the outside of a channel area and within the maximal reconstruction area of a CT scanning device, and storing the theoretical value of the fixed calibration element; collecting the projection data of the fixed calibration element to obtain the actual reconstructed image of the fixed calibration element; and comparing the actual reconstructed image with the stored corresponding theoretical value, to establish a mapping function for correcting the actual reconstructed image into the theoretical value. By adopting the present invention, the calibration quality can be effectively improved, the image calibration effect is enhanced, the reliability of the CT scanning device is improved and the maintenance cost is saved, thus the practical application value is very high.