Congenital pelvic ureteral junction obstruction is the main cause of pediatric hydronephrosis, and the incidence can reach 600 to 800 percent. Diagnosis: 1. Clinical manifestations: The main manifestations are abdominal cystic mass, pain in the lower back and abdomen, and also hematuria and urinary tract infection. 2, related tests: mainly intravenous pyelogram, ultrasound, MRI, etc. Treatment: 1.For mild hydronephrosis with no symptoms, surgery is not necessary and should be followed up regularly. 2.For moderate to severe hydronephrosis, surgery should be performed in time. At present, dissection pyeloplasty is the most reasonable and effective, with a success rate of more than 95%.