Objective:To explore the clinical efficacy and complications of flexible ureteroscopy combined with flexible vacuum-assisted ureteral access sheath(FV-UAS)in the treatment of patients with incarcerated upper ureteral calculi(UDU)with diameter<1.5 cm.Methods:The clinical data of patients with incarcerated UDU with diameter<1.5 cm who received FV-UAS were retrospec-tively analyzed and the patients were included in study group(n=225).The clinical data of 227 patients who used common ureteral access sheath during flexible ureteroscopic lithotripsy were collected during the same period and the patients were set as control group.The perioperative indicators,surgical efficacy,serum levels of inflammatory factors and oxidation factors before surgery and at 3 days af-ter surgery and occurrence of complications were compared between groups.Results:The surgical time and hospitalization time in study group were shortened,and the intraoperative blood loss was reduced,and the stone clearance rate was risen compared with that in control group(P<0.05),and the total effective rate of surgical treatment was higher compared with that in control group(P<0.05).At 3 days after surgery,the levels of serum CRP,IL-10,TNF-α,MAD and AOPP in study group were lower than those in control group(P<0.05)while the levels of serum GSH-PX and SOD were higher than those in control group(P<0.05).The total incidence rate of post-operative complications in study group was lower than that in control group(P<0.05).Conclusion:FV-UAS for incarcerated UDU with diameter<1.5 cm can effectively enhance the clinical efficacy,educe stress reactions caused by surgical trauma,and reduce the postoperative complications.