Ultrasound shows that both renal pelvis are separated, which suggests that there may be fluid or tumor in this area. Normal renal pelvis is not separated and the anterior and posterior diameters of renal pelvis are less than 0.7cm, if it is more than 0.7cm, especially more than 1cm, it is called double renal pelvis separation. The most common cause of double renal pelvis separation is hydronephrosis, which can be caused by many reasons, such as kidney stone, prostate hyperplasia, stenosis of renal pelvic ureteral junction, etc., which leads to urine from the renal pelvis, and the flow of urine is not smooth, and then it will lead to hydronephrosis. Most of the above diseases are treated with surgery, and the hydrocele can be relieved after the cause of the disease is dealt with surgically. In addition to hydronephrosis which can lead to separation of renal pelvis, tumors in kidney can also lead to separation of renal pelvis, once diagnosed with tumors in kidney, surgery should be given positively.