Objective To explore the risk factors of prolonged mechanical ventilation in adult patients after cardiac surgery. Methods The retrospective study enrolled 222 consecutive adult patients undergoing cardiac surgery from Oct 2014 to Jun 2016.Demogra-phic data, perioperative clinical data of heart, lung and kidney function, operation data and postoperative mechanical ventilation time were collected from each patient using a self-designed questionnaire. Results The incidence rate of prolonged mechanical ventilation （＞24 h） was 25.2%.Logistic regression indicated that, NYHA class IV （OR=37.266,P=0.002）, previous cardiac surgery （OR=4.755,P=0.020）, red blood cell transfusion volume during the surgery （OR=1.192,P=0.010）, postoperative ventricular arrhythmia （OR=12.068,P=0.000）, postoperative usage of 1 kind of vasoactive agents （OR=5.139,P=0.000）, postoperative usage of 3 kinds of or more vasoactive agents （OR=8.677,P=0.002）, were risk factors of prolonged mechanical ventilation in adult patients after cardiac surgery. Conclusion The incidence of prolonged mechanical ventilation in adult patients undergoing cardiac surgery is high. Many factors contributed to cause prolonged mechanical ventilation. Measures should be taken to target the risk factors, and nursing care plan should be tailored to the risk factors, so as to shorten the length of mechanical ventilation, and reduce incidence of postoperative complications.