Hydronephrosis is a common disease in pediatric urology, which is mostly caused by congenital urinary tract obstruction, simple dilatation of the renal pelvis or dysplastic kidney. In infants, toddlers and children with hydronephrosis, the prognosis is good with appropriate surgical treatment according to the age and physiological characteristics of the child. The greater the extent or longer the duration of hydronephrosis, the more serious the damage to kidney function. “In the past, it was thought that nephrectomy was indicated for pediatric giant hydronephrosis with thin renal cortex and severely damaged renal units, especially for severe hydronephrosis with fractional renal function <10% and renal cortex thickness <2mm. In recent years, we found through clinical research that the renal function of pediatric severe hydronephrosis has been restored to varying degrees after kidney preservation surgery, which provides new ideas for the surgical treatment of pediatric severe hydronephrosis, so it is more prudent to select the indications for surgical resection of "non-functional kidney" caused by severe hydronephrosis, so as to preserve the kidney unit to the greatest extent. Currently, most pediatric hydronephrosis is detected through prenatal checkups, and the mother of the child has to undergo a great psychological burden in addition to all the hardships during the pregnancy. During the baby's consultation, the most frequently asked question from parents is: Does hydrocele affect the kidney function of the child? Can the kidney still be saved? Clinical observation: some pediatric severe hydronephrosis kidney preservation surgery can be successful. This requires a visit to a professional pediatric urology department to do a comprehensive preoperative evaluation and develop a scientific treatment plan.