Aim To compare the morphological characteristics of culprit lesions in patients with acute ST-segment elevation myocardial infarction (STEMI) and non-ST-segment elevation acute coronary syndrome (NSTEACS).Methods Clinical data of 93 patients accepting coronary angiography and diagnosed with acute coronary syndrome admitted to Henan Provincial People's Hospital from January 2018 to December 2019 were retrospectively analyzed. According to the type of diagnosis, the patients were divided into STEMI group (45 cases) and NSTEACS group (48 cases).During the operation, optical coherence tomography was used to observe the rupture plaque, plaque lipid composition, fiber cap thickness, thrombus type and lumen area of culprit lesions before interventional therapy. Results The proportions of ruptured plaque (68.9% vs 39.6%, P＝0.005), lipid-rich plaque (88.9% vs 68.8%, P＝0.018), thin-cap fibroatheroma plaque (71.1% vs 37.5%, P＝0.001) and red thrombus (73.3% vs 29.2%, P＝0.006) in STEMI group were significantly higher than those in NSTEACS group. The maximum cross sectional area of plaque break in STEMI group was significantly higher than that in NSTEACS group [(2.45±0.65) mm² vs (1.62±1.01) mm²,P＝0.002]. Conclusion OCT show that the morphology of culprit lesions in STEMI and NSTEACS are different, suggesting that the morphology of ruptured plaque and the type of thrombus in coronary artery are related to the clinical manifestations of acute coronary syndrome.