Abstract: Objective To explore the relationship between fractional flow reserve（FFR）and quantitative coronary angiography（QCA）. Methods A total of 135 patients with acute ST-segment elevation myocardial infarction（STEMI）were enrolled in this study,who underwent delayed percutaneous coronary intervention（PCI）and the measurement of FFR. Linear regression analysis was used to assess the relationship between FFR and QCA of the infarct-related artery. Results There were 22 patients with diameter stenosis of 50%-70%,27.3% of which had FFR＜0.80. There were 62 patients with diameter stenosis of 70%-90%,21.0% of which had FFR≥0.80.There were 51 patients with diameter stenosis of 90%-99%,3.9% of which had FFR≥0.80. Pearson correlation analysis showed that parameters of QCA,including diameter stenosis and lesion length were negatively associated with FFR（r=-0.677,-0.538,respectively）,while minimal lumen diameter was positively associated with FFR（r=0.676）,all P＜0.001. Multivariate linear regression analysis revealed that diameter stenosis（B=-0.006）,lesion length（B=-0.009）and minimal lumen diameter（B=0.195）were influencing factors for FFR（all P＜0.001）. Conclusion QCA was associated with FFR in patients with STEMI who underwent delayed PCI.