Left hydronephrosis can be caused by the following reasons: First, if a pregnant woman, the fetus is too large causing the uterus to increase in size, which can then compress the left ureter, causing ureteral occlusion and causing left hydronephrosis, which usually does not require treatment and can be reviewed regularly. Second, kidney tumor, if there is a tumor in the left kidney can destroy the normal structure and function of the left kidney, resulting in hydronephrosis and other symptoms, then anti-tumor treatment should be given, such as tumor removal, radiotherapy, chemotherapy and other treatments, and the hydronephrosis will disappear naturally after the tumor is eliminated. Third, ureteral stones can cause hydronephrosis, which is caused by stones in the left ureter, resulting in inaccessibility of the ureter and causing hydronephrosis in the left kidney, and is usually treated with extracorporeal shock wave lithotripsy and Chinese medicine lithotripsy, and the hydronephrosis in the left kidney will disappear naturally after the stones are discharged.