The most common type of congenital hydronephrosis in children is hydronephrosis caused by stenosis (or obstruction) of the ureteropelvic junction, which often results in progressive enlargement of the hydronephrosis (pelvis) due to stenosis of the ureteropelvic junction, as indicated by ultrasound, an enlarged pelvic separation of the affected kidney, (isotopic fractionation of renal function) a nephrogram showing mechanical obstruction of the affected kidney, a non-decreasing excretion curve after diuresis, and a decrease in the function of the affected kidney. Surgery is mainly to solve the part with lesion, i.e. the narrow part, in order to solve the urine excretion smoothly, to stabilize the degree of hydronephrosis, to stabilize the kidney function, to prevent the further aggravation of hydronephrosis, and to prevent the progressive decline of kidney function, and not to make the hydronephrosis disappear and return to normal, as parents think. Of course, there may be some improvement of hydronephrosis after surgery, but it varies from person to person and depending on the degree of hydronephrosis before surgery, for example, if the hydronephrosis is severe before surgery, it may return to mild or moderate hydronephrosis after surgery. Of course, some children with mild hydronephrosis, but with abdominal pain and hematuria, also need surgery. These children will recover better after surgery, and may have mild hydronephrosis or even no hydronephrosis as indicated by postoperative ultrasound. If the ultrasound indicates a stable or improved degree of hydronephrosis after surgery and the diuretic (isotope) nephrogram indicates an improvement in the function of the affected kidney, the surgery should be considered a success. Of course, before puberty, children still have a growth and development process, therefore, after the post-operative review (ultrasound, isotope) indicates a good recovery, it is recommended to review the ultrasound at least once a year, especially for children with more serious hydronephrosis before surgery. The postoperative ultrasound examination of hydronephrosis should basically include several points: the size of the kidney, the thickness of the cortex, the degree of separation of the renal pelvis (renal calyces), and whether the ureter is dilated. Generally speaking, if the hydronephrosis (dilatation) of the renal pelvis is reduced after the operation, and the child has no abdominal pain, hematuria and other symptoms, it can be said that the operation is successful and the degree of hydronephrosis can be stabilized in the future, and there are usually no sequelae in adulthood.