The invention relates to a post-processing method for removing ring artifacts in a CT (computed tomography) image, and the post-processing method comprises the following steps: converting the CT image with ring artifacts from a rectangular coordinate image to a polar coordinate image; extracting the ring image in polar coordinates with a comb filter in a polar coordinate image domain; converting the ring image extracted out of the polar coordinates to a ring image in rectangular coordinates; and subtracting the ring image in the rectangular coordinates from the original CT image with the ringartifacts to obtain a ring-free image. Through frequency domain comb filtering technology, the post-processing method provided by the invention subtracts the corresponding ring artifact image from the original image, without reduction of image resolution and change of quality of the original image. The post-processing method achieves the processing effect, and meanwhile the speed meets product requirements and has space for further optimization, so that the post-processing method is fully suitable for a CT machine with higher requirements for the reconstruction speed.