【Abstract】Objective To monitor the cuff-pressure of endotracheal tube on patients under CPB anesthesia and discuss its clinical significance. Methods This is a prospective and randomized clinical study. Forty patients undergoing elective surgery under CPB anesthesia with tracheal intubation were divided into 2 groups: 25cmH2O as initial cuff-pressure of endotracheal tube(group A) and 30cmH2O as initial cuff-pressure(group B). The pressure of the tracheal tube cuff was recorded at different temperature points during cooling and warming. Meanwhile, CPB time, circulatory arrest time, postoperative mechanical ventilation time, postoperative hospitalization days and respiratory complications were noted. Results The two groups were comparable with respect to age, sex, body mass index(BMI), CPB time, circulatory arrest time, postoperative mechanical ventilation time, postoperative hospitalization days and respiratory complications. The pressure of the tracheal tube cuff during cooling and warming was significantly different with that at initial temperature. The pressure was significantly higher in group B than in group A at the same temperature points. Conclusion For patients under CPB anesthesia, hypothermia will significantly reduce the cuff-pressure of endotracheal tube, so, monitoring the cuff-pressure of endotracheal tube is very important, it should be routinely measured and controlled for these patients. In clinical practice, both 25cmH2O and 30cmH2O as the pressure of the tracheal tube cuff are safe.