Hydronephrosis is mainly caused by deformity, stenosis, urinary stones (urinary stones, kidney stones, etc.), ureteral tumors and other lesions, which lead to difficulties in urine discharge from the kidneys, among which obstruction of the left urethra is manifested as left hydronephrosis. There are different degrees of left hydronephrosis. Mild left hydronephrosis does not affect kidney function very much and can be cured with timely treatment, but it is very difficult to heal on its own. Clinically, it is mainly called severe hydronephrosis when the amount of hydronephrosis is more than one thousand milliliters or the amount of hydronephrosis exceeds twenty-four hours of urine volume. Once it develops into severe, it will easily cause the pressure in the left kidney to rise and the kidney parenchyma to atrophy, which will have a great impact on people’s health. If it is caused by kidney stones, the stones can be discharged through medication or surgery; if it is caused by ureteral stenosis, ureteral stones, ureteral tumors and other diseases, the causes need to be solved first, that is, treated according to the specific cause of fluid accumulation to restore the urinary tract as soon as possible. If the damage to the kidney is more serious, the left kidney may also need to be removed. In conclusion, most of the clinical patients are easy to ignore the early symptoms of left hydronephrosis, and then miss the better treatment time, resulting in some damage to kidney function. Therefore, for the treatment of left hydronephrosis, the first thing is to find out the cause of urethral obstruction, the most common clinical reason is stone blockage, and release urethral obstruction as soon as possible to avoid further aggravation of hydronephrosis and damage to kidney function.