Objective To evaluate the clinical efficacy of continuous veno-venous hemodiafiltration (CVVHDF) in treating critically ill patients with sepsis and acute renal injury. Methods The clinical features and factors affecting prognosis were retrospectively analyzed in 16 critically ill patients with sepsis and acute renal injury who received daytime CVVHDF in this hospital from Jan. 2009 to Feb. 2009. Patients received this treatment schedule with CVVHDF of 35-40 ml per kilogram of body weight per hour and 1500-2000 ml dialysate per hour. Results Seven patients (43.8%) survived the acute phase of their illness, with APACHE Ⅱ score being 25.4±6.7; whereas nine patients (56.2%) died during the acute phase, with APACHE Ⅱ score being 34.4±4.3. Clinical data, biochemical parameters, mechanical ventilation, characteristics of organ failure, and severity of the illness were analyzed between the two groups. There were significant differences in plasma sodium, urinary volume, number of failure organs and mechanical ventilation between the two groups before CVVHDF treatment (P<0.05). Meanwhile, higher APACHE II score and severer metabolic acidosis were found in the died group. Conclusion Daytime CVVHDF is useful for the decrease of mortality rate in critically ill patients with sepsis and acute renal failure. The prognosis of these patients is correlated to mechanical ventilation, number of affected organs, plasma sodium concentration, metabolic acidosis and APACHE Ⅱ score.