Objective To investigate the risk factors relating to prognosis and to evaluate the clinical situation using APACHE scores in critical patients after surgery and treated with continuous renal replacement therapy (CRRT). Subjects and methods Patients after surgery and treated with CRRT were recruited from several departments in Shanghai Ruijin Hospital affiliated to Shanghai JiaoTong University, School of Medicine during the period of 2004-2007. Their APACHE II and III scores were estimated within 24 hours before CRRT, and their risk coefficient of mortality was also assessed. The software SPSS 15.0 was used for statistical evaluation. Measurement data were shown as X±S, Chi-square test was used for ratio comparison, and one sample t test was used for comparison among groups. P<0.05 was considered to be significant. Multinomial logistic regression was applied to explore the risk factors. Results A total of 86 post-operation patients under CRRT were studied, with the age of 62.2±16.2yrs, 57 males and 29 females, and 54 patients treated in ICU. Thirty-three cases underwent heart surgery including valvular surgery 13 cases and coronary arterial surgery 19 cases, and all of them were complicated with surgery-related acute kidney injury. Twenty-three cases had operations pertinent to general surgery, 18 cases treated with transplantation operations including liver transplantation 16 cases and renal transplantation 2 cases, 6 cases underwent thoracic operation including esophageal operation and pulmonectomy, and 7 cases had operations due to trauma including neurosurgery 5 cases and other operations 2 cases. Of them 29 cases survived, with the mortality rate of 66.3%. The average APACHE II score was 26.3±7.2 in the 86 cases, in which the score was 23.0±5.8 in survival cases and was 27.9±7.3 in dead cases (P<0.01). The average APACHE III score was 67.4±18.0 in the 86 cases, in which the score was 60.0±14.8 in survival cases and was 71.2±18.4 in dead cases (P<0.01). Logistic regression analysis showed that mechanical ventilation (P=0.000) and multiple organ dysfunction syndrome (P=0.033) were the risk factors for the mortality in patients after surgery and treated with CRRT. Conclusion The prognosis of the patients after surgery and treated with CRRT is closely related to APACHE score, with the higher mortality rate in patients with higher score. APACHE score may be useful for the early prediction of mortality in these patients. One of the two APACHE scoring systems is sufficient for the prediction. Patients complicated with multiple organ dysfunction syndrome or treated with mechanical ventilation are at higher risk of mortality