Aim To investigate the correlation between triglyceride-glucose (TyG) index and the severity of coronary artery disease assessed in patients with acute myocardial infarction (AMI). Methods The study restrospectively selected 424 patients with AMI in the Fourth Affiliated Hospital of Xinjiang Medical University from January 2020 to March 2023. Clinical data and results of coronary angiography (CAG) were collected. Gensini score was used to quantitatively assess the degree of coronary artery stenosis. According to tertiles of the Gensini, the patients were classifified into three groups:low Gensini score group (＜45 points, n＝140), medium Gensini score group (45～86 points, n＝143), and high Gensini score group (≥87 points, n＝141). The associations between TyG index and the occurrence of coronary artery disease with high Gensini score by Logistic regression analysis; Spearman correlation was used to analyze the correlation between TyG index and Gensini score in AMI patients; ROC curve was used to analyze the value of TyG index in predicting the severity of coronary artery lesions. Results TyG index of high Gensini score group was significantly higher than that of low and medium Gensini score group (P＜0.05). Logistic regression analysis showed that TyG index was an independent risk factor for severe coronary lesions in AMI patients (OR＝13.7,5%CI:2.642～67.235, P＝0.002). Spearman correlation analysis showed that TyG index was positively correlated with the severity of coronary artery disease (r＝0.331, P＜0.001). ROC curve analysis showed that the area under curve of TyG index was 0.680 (95%CI:0.630～0.731, P＜0.001). When the cut-off value of TyG index was 1.555, the predicted efficacy of of severe coronary artery disease in patients with AMI was the highest, with a sensitivity of 79.4% and a specificity of 50.5%. Conclusion TyG, as a novel biomarker, was significantly and independently associated with the severity of the coronary arteries in patients with AMI.