Objective: To evaluate the phenomenon of post-coronary artery bypass graft (CABG) supply-dependent oxygen consumption and the critical level of oxygen delivery. Methods: 53 patients undergoing CABG were randomized selected for this study. The oxygen delivery, oxygen consumption, and oxygen extraction were studied 1,4,12,24, and 48 hours post-operatively. Data were analyzed by SPSS. Results: The oxygen delivery of post-op 1 hour was the lowest (363.88ml?min -1 ?m -2 ). The 4th and 12th hour post-operatively oxygen deliveries were 396.02 ml?min -1 ?m -2 and 412.92 ml?min -1 ?m -2 respectively, lowers than that post-op 24 hour. After post-op 24 hour, the oxygen delivery was relatively stable, and the value was 468.78 ml?min -1 ?m -2 . The oxygen consumption of post-op 12 hour was the highest (143.02 ml?min -1 ?m -2 ), which closed to the normal value. The oxygen extraction of post-op 1 hour was the highest (35.6%). The oxygen extraction of post-op 12 hour was 32.6%, slightly lower than that post-op 1 hour. The oxygen extraction of after post-op 24 decreases obviously to be relatively stable, the value was 30.2%. Conclusion: 1, Postoperative 1 to 4 hour of CABG, hypoxia exists and oxygen delivery should be increased by maintain a higher pulmonary capillary wedge pressure and cardiac index. 2,There is a pathologic oxygen supply dependency for critical patients of post-CABG, the patients is still in hypoxia post-CABG 48 hour. Therefore, it is very important to keep oxygen supply and decrease oxygen consumption. It is better that the assistant ventilation is kept about 24 hours postoperatively. The pulmonary complications should be controlled as soon as possible. 3, The critical level of oxygen delivery is between 363.88 ml?min -1 ?m -2 and 396.02 ml?min -1 ?m -2 .