Hydronephrosis is the accumulation of fluid in the kidneys. It mainly refers to the accumulation of urine in the renal pelvis and calyces due to urinary tract obstruction caused by various reasons, resulting in urine retention, collectively called hydronephrosis. The symptoms of hydronephrosis are relatively insidious in the early stage, and in the late stage, an abdominal mass or a feeling of swelling in the lower back and pain in the lower back may appear. The clinical symptoms of hydronephrosis are related to the severity of the disease. 1.Mild condition: Patients have no obvious feeling or symptom in early stage, which can be found by checking the ultrasound of urinary system. 2.Serious condition: It is possible to find abdominal mass or waist swelling, painful sensation in the lower back, and the pain is relatively mild, mostly dull pain. 3.Combined infection: If hydronephrosis is combined with infection, there may be symptoms of infection, such as high fever and chills, frequent urination, urgent urination, painful urination, etc. Some patients may also have local renal colic. 4, kidney function damage: long-term hydronephrosis kidney tissue continues to high pressure state, easily lead to atrophy of the kidney parenchyma, resulting in damage to kidney function. Polyuria, oliguria, generalized swelling, hypertension, hypoproteinemia, and other symptoms may occur. Hydronephrosis can lead to infection, which may form abscess kidney or pus in the kidney, all of which are very dangerous.