Ureteral stenosis refers to the narrowing of the lumen of the ureter, which causes abnormal urinary discharge, and further leads to hydronephrosis, and the causes of the corresponding conditions mainly include infection, stones, tumors and congenital development. 1. Infection: Ureteral inflammation will lead to thickening of the ureteral wall, edema and adhesion, which will further lead to ureteral stenosis. 2. Stone: Ureteral stone scratches the ureteral wall, leading to fibrosis and scar tissue formation, which further leads to ureteral stenosis. 3. Tumor: tumors originating in the ureter will lead to the formation of soft tissue mass, which will further lead to ureteral stenosis or even obstruction; tumor lesions around the ureter will cause pressure on the ureter, which will also lead to stenosis. 4. Congenital development: some people will have congenital developmental ureteral stenosis, and most of them will be accompanied by folds and bends of the ureter. If ureteral stenosis is detected and leads to hydronephrosis, it is necessary to consult a doctor in time for observation and standardized treatment under the guidance of a clinician.