In clinical practice, red blood cell infusion needs to be based on the patient′s hemoglobin level. However, different guidelines recommend different thresholds for red blood cell infusion and the timing of blood transfusion initiation is still controversial due to the presence of these different thresholds. Meanwhile, the use of allogeneic blood products carries a certain risk of transfusion-related infections or organ damage. Therefore, initiating red blood cell infusion requires more evidence. This review discusses some new methods, namely central venous oxygen saturation, arterial venous oxygen difference, near-infrared spectroscopy, and perioperative transfusion trigger score. It aims to help evaluate blood transfusion trigger and provide reference for doctors when making transfusion decisions.