Babies with hydronephrosis should be registered with pediatric surgery because hydronephrosis in infants and children is mostly caused by congenital developmental malformation of the urinary system, which can only be resolved by surgery. The child needs timely ultrasound or CT examination of the urinary system to understand the severity of hydronephrosis, and blood needs to be drawn to check the kidney function. If the hydronephrosis is severe or the kidney function is significantly impaired, surgery is needed as soon as possible to facilitate the release of the obstruction and relieve the hydronephrosis, thus protecting the kidney function of the patient.