This study aimed to investigate the outcomes of diagnosis and treatment towards post-Cardiac Surgery (CS)-Delayed Large Pericardial Effusion (DLPE). 62 patients among 8764 cases of cardiac surgery were enrolled in this study. The clinical data of them were summarized. The pericardiocentesis and drainage were performed, with open surgery in partial patients. Before and after treatment, the heart rate, blood pressure and blood oxygen saturation were determined and were compared. The short- and long-term outcomes were observed. Results showed that, among 62 post-CS-DLPE cases, 1 case died of invalid rescue, but the symptoms of the 61 survived patients were significantly mitigated. A total of 800 ± 180 ml of pericardial effusion was drained on the surgery day, and the total amount was 1800 ± 300 ml. There were significant differences of heart rate, systolic blood pressure, mean blood pressure and mean pulmonary artery pressure between before and after treatment (P<0.05). The postoperative 1-month electrocardiograph prompted no pericardial effusion in 57 cases, with small amount of pericardial effusion in 4 cases. The postoperative 6-month and 1-year follow-up revealed no pericardial effusion in all patients. The post-CS-DLPE is easily mis-, miss-, or delay-diagnosed, so the early diagnosis is crucial. Once diagnosed, it should be treated as early as possible, and the treatment effects in most patients are satisfactory.