Objective To evaluate the effects of two filtration fraction formulas on extracorporeal circulation life of continuous renal replacement therapy (CRRT) under regional citrate anticoagulation. Methods Patients with acute kidney injury who received CRRT treatment with regional citrate anticoagulation and the estimated CRRT duration was greater than 24 h at West China Hospital of Sichuan University between June 2022 and April 2023 were selected. They were randomly divided into continuous veno-venous hemofiltration (CVVH), continuous veno-venous hemodialysis (CVVHD) and continuous veno-venous hemodiafiltration (CVVHDF) groups using Prismaflex machines. The life of the CRRT extracorporeal circulation in the three groups of patients was compared, and the reasons for replacing the extracorporeal circulation after 72 h were not used, and the filtration fraction score of the three groups was calculated according to the two filtration score calculation formulas (Formula 1 and Formula 2) currently used in the world. The filtration value obtained by the two filtration fraction calculation formulas was taken as the test variable, and whether the median life of the group with the longest extracorporeal circulation life was taken as the state variable, and the receiver operating characteristic curve was drawn, and the area under the curve was calculated. Results A total of 121 patients were included, including 40 patients in the CVVH group, 40 patients in the CVVHD group, and 41 patients in the CVVHDF group. The extracorporeal circulation life of CVVH group, CVVHD group and CVVHDF group was 64 (46, 71) h, 47 (31.5, 54) h and 70 (65, 72) h, respectively, with statistical difference (log-rank P=0.036). A total of 94 cases were replaced due to filter or venous pot clotting after 72 h after the filter was not used, including 30 cases in the CVVH group, 39 cases in the CVVHD group, and 25 cases in the CVVHDF group. The difference between the three groups was statistically significant (χ2=15.83, P<0.001). According to Formula 1, the filtration fraction of CVVH group, CVVHD group and CVVHDF group was 15.8% (15.2%, 17.0%), 1.1% (0.7%, 2.1%) and 16.2% (14.9%, 17.6%), respectively, and the difference among the three groups was statistically significant (H=69.402, P<0.001). According to Formula 2, the filtration fraction of CVVH group, CVVHD group and CVVHDF group was 33.1% (32.4%, 35.7%), 4.0% (3.6%, 4.9%) and 19.1% (17.7%, 20.7%), respectively, and the differences among the three groups and pairwise comparison between groups were statistically significant (P<0.001). The area under the receiver operating characteristic curvec calculated by the Formula 1 and 2 for the influence of filtration fraction on extracorporeal circulation life were 0.539 and 0.668, the sensitivity were 43.18% and 82.22%, and the specificity were 80.65% and 56.25%, respectively. Conclusions When using Prismaflex machine, the filter life of CVVHD is shorter than CVVH and CVVHDF modes. The filtration fraction calculated by Formula 2 is more sensitive but less specific in predicting CRRT extracorporeal circulation life. Filtration fraction as a CRRT extracorporeal circulation risk assessment has limitations, especially for the CVVH model with pre and post replacement.