Fractional flow reserve (FFR) is a gold standard for the assessment of hemodynamic change during coronary stenosis, but it has several limitations such as high cost, the requirement of invasive pressure wire, and adverse drug reactions, which limit the wide application of FFR in clinical practice. In contrast, quantitative flow ratio (QFR) is a recently developed method for rapid calculation of FFR through 3-dimensional quantitative coronary angiography without the use of vasodilators and pressure wire. In this review we provide an updated summary of the principle of QFR, the correlation between QFR and FFR, and current applications of QFR in clinical cardiology. In conclusion, QFR provides a platform for functional evaluation of coronary stenoses based on angiographic data without invasive procedures; further development and optimization of QFR techniques will expand the application of QFR in clinical cardiology, ranging from diagnosis to coronary intervention to cardiac surgery, and benefit more patients.