Objective To explore the value of post-processing technique of multi-slice spiral computed tomography (CT) in the diagnosis of carotid atherosclerotic plaques. Methods The clinical data of 72 patients with suspected carotid atherosclerotic plaque were retrospectively analyzed. All patients were diagnosed by postprocessing technique of multi-slice spiral CT and were examined by digital subtraction angiography (DSA). The results of detection and diagnosis of carotid atherosclerotic plaque by multi-slice spiral CT post-processing technology were analyzed. The results of two diagnostic methods for carotid stenosis were analyzed. The results of DSA in the diagnosis of carotid stenosis are the golden standard. The post-processing technology and consistency of multi-slice spiral CT was analyzed. Results A total of 56 cases of carotid atherosclerosis plaques were detected in this group, totally 116 plaques found, of which carotid bifurcation plaques accounted for the most (49.18%) and soft plaques accounted for the highest (52.59%). At the bifurcation of carotid artery, the proportion of soft plaque was the highest (35.34%), mixed plaque was the second (10.34%), and calcified plaque was the lowest (3.45%). There were 576 segments of bilateral carotid arteries in 72 patients. The results of multi-slice spiral CT post-processing showed that there were 256 no stenosis segments, 111 slight stenosis segments, 162 moderate stenosis segments, 45 severe stenosis segments, and 2 complete occlusion segments. One segment was diagnosed as mild stenosis without stenosis by multi-slice spiral CT post-processing technology; one slight stenosis was diagnosed by DSA and no stenosis was diagnosed by multi-slice spiral CT post-processing technology. The coincidence rate was 99.65%. There was a good consistency between them (κ = 0.912, P = 0.007). Conclusion For the diagnosis of carotid atherosclerosis plaque, multi-slice spiral CT post-processing technology is helpful to understand the number and nature of plaque, and the diagnosis of carotid stenosis is consistent with DSA.