If a child still has moderate hydronephrosis 3 years after hydrocele surgery, it may be due to the long-term preoperative hydronephrosis that causes the structure of the renal pelvis and renal calyces to dilate and change, and usually this change is irreversible, so when doing the imaging examination, the imaging physician will see the dilation of the structure of the renal pelvis and renal calyces, which is usually considered as the possibility of hydronephrosis. Pediatric congenital hydronephrosis is usually caused by ureteral or renal pelvis structural underdevelopment, stenosis, or congenital compression by large blood vessels, etc. Surgery is often used to relieve obstruction and restore renal function when obstruction is caused. Children with hydronephrosis 3 years after surgery or moderate hydronephrosis should be considered comprehensively, check whether the child’s renal function is abnormal, whether there is obstruction in the urinary system, etc., and once the problem is detected, it should be treated in regular hospitals to avoid delaying the condition.