Hydronephrosis is a dilatation of the renal pelvis caused by urine being retained in the renal pelvis due to urinary tract obstruction. The difficulty of treatment for hydronephrosis is directly related to the cause of hydronephrosis. There is a direct relationship between the treatment for hydronephrosis and the difficulty of treatment and the cause of hydronephrosis. The possible causes of nephrolithiasis include physiological causes and pathological causes. The physiological cause is mainly caused by pregnancy. If the hydrocele is caused by an increase in the size of the uterus of a woman in the second trimester, most of them do not require treatment if there are no obvious symptoms, and the hydrocele will gradually subside after normal delivery. Pathological causes include urethral stones, ureteral stones, prostatic hyperplasia obstruction, tumor, urinary system malformation, etc. If the hydrocele is caused by urethral stones, ureteral stones, prostatic hyperplasia obstruction, it is relatively easy to treat, only need to remove the stones and restore the smoothness of urethra and ureter to relieve the hydrocele. However, if the hydrocele is caused by tumor or urinary system malformation, such as ureteral tumor, bladder tumor, prostate cancer, or tumor outside the urinary system, such as abdominal tumor, pelvic tumor compression or invasion of the ureter, it will be more difficult to treat the hydrocele.