Physiological hydronephrosis in infants usually disappears on its own before the age of 2 years, but there are individual differences and regular follow-up is needed, and pathological ones usually cannot disappear on its own. Pediatric hydronephrosis is divided into physiological and pathological. If the hydronephrosis is physiologic, it will gradually disappear with age. If pathologic hydronephrosis is formed due to dilatation of the renal pelvis and renal calyces caused by obstruction of the urinary system, timely treatment is needed. After the discovery of hydronephrosis in infants, the degree of hydronephrosis should be assessed by ultrasound. If it is within 1 cm and there are no obvious symptoms, it can be rechecked once every three months, and the disappearance of hydronephrosis confirmed by ultrasound for two consecutive times can be considered as a self-cure. If the infant’s hydronephrosis causes compression of renal tissues, resulting in renal function damage, or even the absence of urine, this situation needs to go to the pediatric internal medicine department in time for consultation and treatment.