1, hydronephrosis due to pelvic ureteral junction obstruction (UPJO): It means that urine cannot enter the ureter from the renal pelvis smoothly, causing progressive expansion of the renal collecting system. UPJO is the most common cause of hydronephrosis in newborns, accounting for more than 85% of cases, more in males than females, and more on the left than on the right. (3) Clinical manifestations: (1) Fetal hydronephrosis can be detected by ultrasound during pregnancy, and regular follow-up B-ultrasound is required after birth. (2) Other children have no special symptoms in the early stage, the main manifestations of serious obstruction are: (1) abdominal mass: mostly seen in newborns or infants, smooth mass, no pressure pain, mass reduction after a lot of urination is an important diagnostic basis; (2) intermittent pain in the lumbar abdomen: older children can clearly point out that the pain comes from the affected side of the lumbar area, can be induced after a lot of water; (3) hematuria: trauma, combined urinary tract infection or renal medulla (3) hematuria: trauma, combined urinary tract infection or renal medulla can lead to hematuria. (4) Treatment: (1) Mild hydronephrosis with no obvious clinical symptoms can be followed up and observed. (2) Progressive enlargement of hydronephrosis, as well as obvious evidence of UPJO or progressive kidney damage should be treated surgically. 3) If hydrocele is found in the fetus, about 1/3 of the children can be normalized after birth. 5.Operation purpose: To remove the diseased segment of ureter and a small part of renal pelvis and reconstruct the ureteropelvic junction so that urine can flow smoothly into the ureter. 6.Operation age: Those who need surgery are generally not restricted by age.