Mild hydronephrosis of the left kidney usually does not need treatment, and can be treated by giving extracorporeal lithotripsy or minimally invasive surgery to remove the stone and resect the stenotic segment after clarifying the cause of the disease, such as ureteral stone, urinary tract infection, ureteral stenosis and other causes. 1. Ureteral stone: It is mainly due to the stone embedded in the ureter, blocking the urinary tract and thus causing hydronephrosis. Depending on the size of the stone, we can choose medication, extracorporeal lithotripsy, intervention or open surgery to remove the stone. 2. Urinary tract infection: If urinary tract infection occurs repeatedly, it may cause the ureter to become narrower and narrower, thus leading to hydronephrosis. You can take drugs such as cefixime granules, amoxicillin capsules, or luminal surgery, balloon dilatation, to improve the state of ureteral adhesion. 3. Ureteral stenosis: Ureteral stenosis will cause urinary tract obstruction, accumulation of urine in the kidney and increased pressure leading to hydronephrosis. It can be treated by surgically removing the narrowed segment to ensure the patency of the ureter. In conclusion, mild hydronephrosis needs to go to the hospital in time, improve the examination of the cause of the disease under the guidance of the doctor, and treat the symptoms.