When to do surgery for pediatric hydronephrosis is best determined by the severity of the condition itself. At present, it is believed that whether or not to perform surgical treatment is mainly determined by the following three aspects: First, if the kidney function of the child is less than 40% it needs to be operated immediately, and if surgery is not done soon, the kidney function may further deteriorate or even develop uremia. Second, if the child has obvious anatomical evidence, that is, a clear obstruction of the renal pelvis and ureter is found clinically through ultrasound, CT and other related examinations, then surgery must be performed as soon as possible. If the child has vomiting, abdominal pain, or hematuria, surgery can also be considered.