Objective：To observe the effects of sustained inhalation of low concentrations of oxygen and pure oxygen on perioperative myocardial injury in patients undergoing off-pump coronary artery bypass grafting（OPCABG），it is proposed to investigate the optimal fraction of inspired oxygen（FiO₂）in patient undergoing OPCABG. Methods：A total of 100 patients with OPCABG that are aged 48 to 78 years，body mass index（BMI）of 21.7 to 33.9 kg/m² ，and American society of anesthesiologists physical status classification system（ASA) grade Ⅲ~Ⅳ were selected. They were divided into 2 groups：low-concentration oxygen group（L group，n=49）and pure oxygen group（H group，n=51）using random number table. After the routine anesthesia induction of propofol and fentanyl combined with cis-atricuronium and mechanical ventilation after endotracheal intubation，the inhaled oxygen concentrations of the two groups were adjusted to 40% and 100%，respectively，and maintained until the end of the operation. Volume controlled ventilation mode was used during the operation，with a tidal volume of 6~8 mL/kg and an I/E ratio of 1∶2. Two groups of patients were given total intravenous anesthesia：continuous infusion of propofol，dexmedetomidine，and cis-atriammonium，intermittent infusion of fentanyl，to maintenance the BIS values of 40~60 during the operation. Blood samples were collected from the upper limb of patients on the day before surgery（T₁），after induction of anesthesia（T₂），at the end of surgery（T₃），the first day after surgery（T₄），and the third day after surgery（T₅）. The concentration of serum creatine kinase-MB（CK-MB）and pro brain natriuretic peptide（proBNP） were measured. Transthoracic echocardiography（TTE）or transesophageal echocardiography（TEE) examination was performed at each time point. The left ventricular ejection fraction（LVEF）value and cardiac output（CO）value were measured by Simpson method. The duration of postoperative mechanical ventilation，ICU stay and total hospital stay were recorded. Results：Compared with T₁，the concentration of serum CK-MB in group L and group H was increased at T_3-5，and the concentration of serum proBNP was increased at T_{2 -5}. Compared with group L，the concentration of CK-MB was increased at T_3-5，and the concentration of proBNP was increased at T_2-5 in group H（P < 0.05）. Compared with T₁，LVEF value and CO value decreased at T₂ in group L and H，LVEF value and CO value increased at T_4-5 in group L，LVEF value and CO value increased at T₅ in group H，LVEF value and CO value decreased at T_4-5 in group H（P < 0.05）. Compared with group L，the mechanical ventilation time of patients in group H was prolonged（P < 0.05），and there was no significant difference in the length of ICU stay and total hospital stay between the two groups（P > 0.05）. Conclusion：Continuous inhalation of 40% oxygen during OPCABG in patients can help reduce myocardial injury within 3 days after surgery and improve left heart function.