Objective To evaluate the diagnostic value of 128-row 256-slice spiral CT angiography (CTA) in carotid artery stenosis, carotid plaque formation and collateral circulation formation in patients with ischemic stroke. Methods A total of 42 patients with ischemic stroke admitted to our hospital from April 2016 to April 2018 were selected. All patients were with the images data of 128-row256-slice spiral CTA and digital subtraction angiography (DSA). The diagnostic results of DSA were set as gold criteria to evaluate the diagnostic value of CTA in carotid artery stenosis, carotid plaque formation and collateral circulation formation. Results A total of 242 vascular segments were evaluated for stenosisdegree in 42 patients, and the coincidence rate of CTA and DSA was 85.12% (206/242). CTA was highly consistent with DSA in the diagnosis of normal, severe and occluded carotid stenosis(K=0.84, 0.75, 0.87), and CTA was moderately or highly consistent with DSA in the diagnosis of mild and moderate carotid stenosis(K=0.69, 0.65). There were no significant differences in the detection rate of carotid atherosclerotic plaque and plaque morphology by DSA and CTA(P＞0.05). The sensitivity, specificity, accuracy, positive predictive value and negative predictive value of CTA in the diagnosis of collateral circulation formation were 88.89%, 86.67, 88.10%, 92.31% and 81.25%, and CTA and DSA were highly consistent in the diagnosis of collateral circulation(K=0.745). Conclusion 128-row 256-slice spiral CTA has good diagnostic value for carotid artery stenosis, carotid plaque formation and collateral circulation formation in patients with ischemic stroke, and it can provide a basis for clinical diagnosis and treatment.