After laser lithotripsy, it is usually necessary to place a double J tube for the following purposes: 1. drainage: because the ureter may be edematous when passing through the ureteroscope, especially some ureteral sites are thin, the ureteroscope may rub the ureter causing edema. The placement of double J tube can let the ureter get sufficient rest and also reduce the patient’s postoperative discomfort; 2, relaxation and dilation of the ureter: this relaxation and dilation effect is continuous, and after the double J tube is removed, the ureter is still in a dilated state, so it is easier to discharge if the stone falls.