Objective To explore the clinical value of CT angiography (CTA) in patients with acute coronary syndrome (ACS) before and after interventional therapy. Methods The clinical data of 126 ACS patients undergoing interventional therapy were retrospectively analyzed. Digital subtraction angiography (DSA) was used as the gold standard to analyze the accuracy of CTA in the grading diagnosis of postoperative vascular stenosis degree in patients with ACS. According to the occurrence of in-stent restenosis (ISR) within 6 months after operation, the patients were divided into ISR group (n=22) and control group (n=104). The accuracy of CTA in the diagnosis of postoperative ISR classification was analyzed, and the CTA quantitative parameters were compared between the two groups. Results Among 126 patients with ACS, 245 coronary artery lesions were diagnosed by DSA before operation, and the accuracy of CTA for stenosis degree grading was 87.76% (215/245), and the accuracy for postoperative ISR classification was 78.57% (99/126). The CT fractional flow reserve (FFRCT) and transluminal contrast attenuation gradient-corrected contrast opacification (TAG-CCO) in ISR group after operation were significantly lower than those in control group (P<0.05). Conclusion CTA can accurately classify the vascular stenosis degree before interventional therapy for ACS patients, and make early qualitative and quantitative evaluation for ISR during postoperative followup, and it is conducive to the development of reasonable interventional therapy and the improvement of prognosis.