Objective：To explore the correlation between operation time and renal function deterioration of flexible ureteroscope in treating renal stones in a solitary kidney postoperatively. Methods：From January 2013 to December 2016，patients with renal stones in a solitary kidney were treated with fURS and followed up for one year in our hospital. Patients whose serum creatinine had elevated obviously were taken as control group and the other patients were as study group. Operation time and serum creatinine one month and one year after operation were recorded. Other parameter including age，gender，body mass index，stone size，number of procedures，stone free rate，hydronephrosis，hypertension and diabetes were analyzed. Results：A total of 42 patients were included in the retrospec－tive study：33 patients were in the study group and 9 patients were in the control group. There was no statisticallydifference in factors such as age，gender，body mass index，number of procedures，stone free rate，hydronephrosis，hypertension and diabetes had（P>0.05）. Other factors such as stone size，operation time and postoperative infection-related complication were higher in the control groupthan in the study group（P<0.05）. Preoperative serum creatininehad no statisticallydifference between the two groups（P>0.05）. But postop－erative serum creatinine in the control group one month and one year after operation were higher than that in the study group（P<0.05）. The area under the receiver operating characteristic curve of operation time in predicting the deterioration of renal function was 0.78 and the cutoff point was 56minutes（95%CI=0.617 to 0.950），in which the sensitivity and specificity were respectively 81.8% and 66.7%. Conclusion：Flexible ureteroscope was a safe treatment method for renal stones in solitary kidney at one year follow-up. But operation time should be controlled within 56minutes. Otherwise，kidney function will be damaged irreversibly and eventually lead to the deterioration of renal function.