Background: In patients with ST-segment elevation myocardial infarction (STEMI) and multivessel disease (MVD), the treatment strategy for non-infarct-related artery (non-IRA) remains controversial. Quantitative flow ratio (QFR) is a new angiography-based physiological assessment index. However, there is little evidence on the practical clinical application of QFR. Methods: Two hundred and twenty-nine patients with STEMI and MVD were recruited for this study. Patients were randomly assigned to either receive QFR-guided complete revascularization (QFR-G-CR) of non-IRA or receive no further invasive treatment. The primary (1 degrees) endpoint analyzed included death due to all causes, non-fatal myocardial infarction (MI), and ischemia-induced revascularization at 12 months post-surgery. Secondary (2 degrees) endpoints included cardiovascular death, unstable angina, stent thrombosis, New York Heart Association (NYHA) class IV heart failure, and stroke at 1 year post surgery. Massive bleeding and contrast-associated acute kidney injury (CAKI) were used as safety endpoints. Results: Around the 12 month follow up, the 1o outcome was recorded in 11/115 patients (9.6%) in the QFR-G-CR population, relative to 23/114 patients (20.1%) in the IRA-only PCI population (hazard ratio [HR]: 0.45; 95% confidence interval [CI]: 0.22-0.92; p = 0.025). Unstable angina in 6 (5.2%) and 16 (14.0%) patients (HR: 0.36; 95% CI: 0.14-0.92; p = 0.026), respectively. No marked alterations were found in the massive bleeding and CAKI categories. Conclusions: In conclusion, STEMI and MVD patients can benefit from QFR-G-CR of non-IRA le- sions in the initial stages of acute MI. This can help reduce incidences of major adverse cardiovascular events and unstable angina, relative to IRA treatment only. Chinese Clinical Trial Registration number: ChiCTR2100044120. (Cardiol J)