The patient was admitted to the hospital on July 29, 2008, with a denial of history of urological trauma and inflammation. He denied any history of urinary trauma or inflammation. Physical examination: abdomen was flat and soft, without pressure pain or rebound pain, and percussion pain in the left kidney area was obvious. After admission, ultrasound showed a left renal pelvis separation of 175 px, and KUB+IVP showed a long segmental stenosis of the left middle and upper ureter (Figure 1), with good renal function. On August 22, the left ureter was enlarged with a rotating tipped pelvic flap under general anesthesia, and the dilated renal pelvis was exposed through an oblique incision under the twelve-rib margin, and the ureter was free of the stenotic segment, which was about 250 px. The stenotic ureter was dissected longitudinally and extended past the pelvic-ureteral junction to the renal pelvis. Depending on the length of the ureteral stenosis, the long tongue-shaped, wide-tipped pelvic flap wall, 37.5 px wide and 275 px long, is intercepted from the top to the bottom along the longitudinal axis of the dilated pelvis, with the portion of the flap attached to the ureter retained. The downward-flipped pelvic flap was laterally anastomosed with the longitudinally dissected ureter of the original stenosis, and a D-J tube ureter was placed and the UPJ was shaped, while a pelvic skin fistula was performed. The nephrostomy tube was removed 2 weeks after surgery, and the D-J tube was removed 3 weeks after surgery. The left hydronephrosis was gradually reduced by regular postoperative follow-up ultrasound. The KUB+IVP was reviewed 1 year after surgery, and the left hydronephrosis was significantly reduced, and there was no significant ureteral stenosis. If the ureteral obstruction is not removed surgically, the hydronephrosis will be further aggravated, which will eventually lead to impaired renal function or even renal failure on the affected side. Ureteral stenosis segment resection anastomosis alone can only solve short distance stenosis, for such long segment ureteral stenosis, performing stenosis segment resection ureteroplasty will inevitably result in insufficient length of ureter after resection. For this patient, with severe hydronephrosis and obvious dilatation of the renal pelvis, it is advisable to replace ureteral enlargement with ureteroplasty after flap reversal. The incision and trauma of this procedure are equivalent to that of a simple ureteral stenosis resection anastomosis, and the flipped pelvic flap not only has a good blood supply, but is also long enough to replace the stenotic ureter. From the clinical point of view, it solves the problem that the ureteral stenosis is too long for direct resection and formation of the stenotic segment; moreover, after pelvic formation, the upper segment of the ureter enlarged by the flipped pelvic flap has no angular deformity and conforms to the normal ureteral curve. In this patient, the ureteral stenosis section was 250 px long and the intercepted pelvic wall flap was 275 px long. Therefore, the pelvic wall flap retained at the base of the pelvis must be wide enough to prevent tissue necrosis, resulting in surgical failure. The peripelvic drainage tube should be kept open to prevent leakage of urine.