Objective To improve the efficiency and safety of replacing circuit and filter in continuous blood purification (CBP) for elderly critically ill patients. Methods Forty-one elderly critically ill patients on CBP were randomly divided into a control group of 20 and an observation group of 21. The control group was given routine circuit and filter replacement for 69 times, while the observation group received 65 times of circuit and filter replacement following the double-machine replacement protocol. Results The observation group had significant reduction in circuit replacement time and smaller blood pressure fluctuations during the replacement process compared with the control group (all P<0.05). There was no significant difference in heart rate fluctuations between the two groups (P>0.05). Conclusion Application of the double-machine circuit replacement method in CBP for elderly critically ill patients can improve circuit replacement efficiency and stabilize hemodynamics.