Separation of the renal collecting system is usually understood as a dilation of the lumen of the kidney that collects urine, including the collecting ducts, calyces, and renal pelvis. A separation of the renal collecting ducts of more than 9 mm is usually clinically significant, therefore, a separation of the right renal collecting ducts of 23 mm is problematic and usually indicates hydronephrosis. Hydronephrosis is mainly caused by urinary tract obstruction, and the most common cause of urinary tract obstruction is the ingrown urinary tract stone. When urinary stones become embedded, the urine is not discharged well and accumulates in the renal collecting system, causing hydronephrosis, which leads to separation of the renal collecting system. In addition to urinary stones, congenital ureteral developmental abnormalities, urinary tract infections, and mass compression may lead to urinary tract obstruction. Therefore, if patients find the separation of renal collecting system, it is recommended to go to regular hospitals in time, improve the examination to clarify the cause of the disease, and then give targeted treatment or therapy under the guidance of doctors.