Objective To analyze the causes and find tactics in ambulatory continuous peritoneal dialysis with ultrafiltration failure. Methods Fifteen patients of ambulatory continuous peritoneal dialysis (CAPD) with ultrafiltration failure (UFF) were enrolled. Frequency and dosage of daily CAPD, ultrafiltration volume and urine volume were recorded. Peritoneal equilibrium test (PET) were performed. Blood pressure, serum creatinine, blood urea nitrogen and blood albumin were measured before and after treatment of UFF. When UFF occurred, routine analysis, bacteria culture of abdominal fluid and color Doppler were performed. Results The causes of UFF included: as follow ① The compliance of peritoneal dialysis prescription was poor; ② The diet of patients was not reasonable. Intake of water and salt was excessive especially; ③The function of remnant nephrons decreased progressively; ④ The irreversible pathologic physiologic course played a role in UFF; ⑤ Peritonitis was a common reason of UFF; ⑥ Peritoneal ultrafiltration function was reduced; ⑦ Malnutrition was indirect cause of UFF. The data showed that the increasing of filtration volume, decreasing of blood pressure, and increasing of serum albumin level occurred after amelioration of UFF(P<0.01). Conclusions The causes of CAPD with UFF were multifarious. Ultrafiltration failure resulted in poor prognosis of patients with UFF. Various measures which aimed at various causes of UFF were performed. The effective therapy of UFF was prevention.