Qbjective: To explore the common causes and treatment of difficult insertion of working sheath in flexible ureteroscopic surgey. Methds: From July 2016 to December 2018

among which 24 cases had the difficulty in placing the working sheath of flexible ureteroscope were analyzed. Results: One-stage flexible ureteroscopic surgery was performed for 113 cases

and there were 21 cases（18.58%

21/113） with the difficulty in placing the working sheath

among which 19 cases were successfully treated by intraoperative techniques and 2 cases were successfully treated by indwelling ureteral stent and second-stage surgery. Second-stage surgery with reserved ureteral stent was performed for 122 cases

among which there were 3 cases（2.45%

3/122） with the difficulty in placing the working sheath. As for the incidence rate of surgical complications

there were 10 cases of grade 1 or 2 complications and 1 case of grade 3 complication in the one-stage surgery

while there was 1 case of grade 1 complication in the second-stage surgery. Two cases of urinary sepsis were observed after the one-stage surgery

and reexamination at 3 months after surgery showed a stone clearance rate of 86.7% in the one-stage surgery and 93.3% in the secondstage surgery. Intravenous pyelography performed at 6 months after surgery showed 2 cases of ureteral stricture in the one-stage surgery

while no case of ureteral stricture was observed in the second-stage surgery. Conclusions:Ureteral stent placement before flexible ureteroscopic lithotripsy can effectively reduce the number of cases with difficulty in working sheath placement and improve surgical safety and stone clearance rate.