Objective To investigate the effects of continuous renal replacement therapy (CRRT) on levels of serum cystatin C (CysC), glomerular filtration rate (GFR) and circulating reninangiotensinaldosterone system (RAAS) of patients with sepsis and acute kidney injury (AKI) and their relationships with prognosis. Methods 76 patients with sepsis and AKI admitted to the hospital from September 2016 to October 2018 were enrolled in the study. They were randomly divided into observation group (n=38) and control group (n=38), according to the random number table method. The control group was given routine treatment. On this basis, the observation group was treated with CRRT. The changes of levels of Cys C, GFR, circulating RAAS and scores of acute physiology and chronic health evaluation (APACHE Ⅱ) in the two groups before treatment and at 3 days after treatment were compared. Correlation between levels of Cys C, GFR, circulating RAAS and APACHE Ⅱ scores and risk factors of prognosis were analyzed. Results After treatment, the levels of Cys C, PRA, AngⅠ, ALD and scores of APACHE Ⅱ in the observation group were lower than those in the control group, while the GFR level was higher than that in the control group (P＜0.05). There were 55 casessurvived in the two groups undergoing treatment for 28 days. The levels of Cys C, PRA, AngⅠ and scores of APACHEⅡ of survivors were lower than those of dead patients, while the GFR level was higher than that of dead patients (P＜0.05). Cys C, PRA and AngⅠ were positively correlated with APACHE Ⅱ scores (r=0.602, r=0.524, r=0.485,P＜0.05), while GFR was negatively correlated with APACHEⅡ scores (r=-0.664, P＜0.05). Univariate and multivariate Logistic regression analysis showed that Cys C, PRA, AngⅠand APACHE Ⅱ scores were risk factors affecting the prognosis of patients with sepsis and AKI, while GFR was a protective factor affecting the prognosis of patients with sepsis and AKI (P＜0.05).Conclusion CRRT for patients with sepsis and AKI can effectively reduce the levels of Cys C, PRA, AngⅠ and increase the level of GFR. And the above indicators are closely related to the prognosis of patients, which are important factors affecting prognosis.