【Objective】 To investigate the effect of optimized preoperative hemoglobin (Hb) level on clinical outcome in patients undergoing coronary artery bypass grafting (CABG). 【Methods】 Retrospective analysis was performed on patients who were selected to receive CABG from April 2020 to August 2021 in our hospital. Preoperative basic data, perioperative blood transfusion volume, blood transfusion rate, acute liver function impairment, renal function impairment (AKI), ICU stay, length of hospital stay, and in-hospital mortality of patients, meeting the inclusion criteria, were collected. According to the perioperative red blood cell transfusion, the optimal preoperative Hb threshold was calculated by receiver operating characteristic curve (ROC). According to the threshold, all patients were divided into two groups, and the blood transfusion volume and clinical outcomes of the two groups were compared to evaluate the predictive value of the optimal threshold of Hb. 【Results】 A total of 915 patients who met the inclusion criteria were enrolled in the study. The optimal threshold for predicting red blood cell transfusion rate by calculating preoperative Hb value by ROC curve was 118 g/L for males and 116g/L for females. Group A: Hb≤ threshold (n=293) was divided into the red blood cell transfusion group A1 and the red blood cell non-transfusion group A2. Group B: Hb>threshold (n=622) was divided into the red blood cell non-transfusion group B1 and no red blood cell non-transfusion group B2. The risk factors for perioperative red blood cell transfusion were age (OR=1.033 874, 95%CI 1.000 4-1.068 3, P<0.01), gender (female) (OR=3.268 5, 95%CI 2.353 1-4.540 0, P<0.01), BMI (OR=0.927 8, 95%CI 0.883 3-0.974 4, P<0.01), chronic renal insufficiency (CKD) (OR=2.041 1, 95%CI 1.347 8-3.091 0, P<0.01). Preoperative Hb≤ threshold (OR=3.517 4, 95%CI 2.502 1-4.944 7, P<0.01) was an independent risk factor for perioperative red blood cell transfusion. Perioperative red blood cell transfusion in patients with preoperative anemia further increases the incidence of postoperative complications (acute liver injury, AKI) and length of ICU stay. 【Conclusion】 Preoperative Hb≤ threshold can effectively predict perioperative red blood cell transfusion in patients with CABG, and increase the risk of postoperative acute liver injury, AKI, prolonged ICU stay and hospital stay. Optimizing the preoperative Hb level in CABG patients, increasing the Hb level to 118 g/L in males and 116 g/L in females can reduce the incidence of perioperative red blood cell transfusion and postoperative complications.