Objective To investigate incidence and modifiable risk factors of postoperative delirium (POD) in patients undergoing cardiac surgery. Methods A prospective observational research method was conducted on 880 cardiac surgery patients admitted to the Department of Cardiovascular Surgery, at the First Affiliated Hospital of Chongqing Medical University from January 2022 to June 2023. Patients' general and clinical data were collected. POD was assessed twice daily from the second day in the ICU using the Confusion Assessment Method of Intensive Care Unit(CAM-ICU) until discharge or transfer from ICU. The patients were divided into two groups based on the presence of POD, and the incidence rate was calculated. Subsequently, a 1:1 propensity score matching (PSM) was applied between the two groups. The differences in general information and clinical characteristics between the two groups of patients before and after PSM were compared. Logistic regression analysis was used to evaluate the modifiable risk factors for POD in patients undergoing cardiac surgery after PSM. Results Of the 880 patients, 278 experienced POD during their stay in the ICU, with an incidence rate of 31.6%. POD occurred between the 2nd and 12th day following ICU admission, with 91.4%(254 patients) experiencing it between the 2nd and 6th day. Univariate analysis identified preoperative factors of POD including gender, age, history of hypertension, history of diabetes, and smoking history; Intraoperative factors were ASA anesthesia grade, operation duration, extracorporeal circulation time, and aortic occlusion time; Postoperative factors included ICU length of stay, mechanical ventilation duration, and VAS score, all of which were statistically significant (P<0.05). After PSM, the distribution of three immutable demographic factors including gender, age, and blood type tended to be consistent among groups (P>0.05). Further multivariate logistic regression analysis showed that surgical time, ICU stay time, mechanical ventilation time, and VAS score were independent modifiable risk factors for POD in cardiac surgery patients (P<0.05), with corresponding OR values of 1.003, 3.117, 1.385, and 1.590, respectively. Conclusions Surgical time, ICU stay time, mechanical ventilation time, and VAS score are independent modifiable risk factors for the occurrence of POD in patients undergoing cardiac surgery. In clinical work, early intervention should be carried out based on the characteristics of the patient's condition and risk factors to further reduce the occurrence of POD.