Hydronephrosis is a common urological lesion with insidious symptoms in the early stage and may appear as an abdominal mass or a sensation of lumbar swelling or pain in the lower back in the late stage. Hydronephrosis mainly refers to the accumulation of urine in the renal pelvis and calyces due to urinary obstruction from various causes, resulting in urine retention, collectively known as hydronephrosis. The most common cause of the appearance of hydronephrosis is obstruction at the junction of the renal pelvis and ureter, such as tumor occupancy and stone obstruction. The clinical symptoms of hydronephrosis are related to the severity of the disease. Patients mostly have no obvious sensation or symptoms in the early stage, and rely on examination of the urinary system ultrasound to detect it. Until the condition is serious, it is possible to find abdominal masses or a feeling of swelling in the lower back, painful sensation in the lower back, and the pain is relatively mild, mostly dull pain. If combined with infection, there may be symptoms of infection, such as high fever and chills, frequent urination, urgent urination and painful urination, etc. Some patients may also have localized renal colic. After long-term hydronephrosis, the kidney tissues are in a state of continuous high pressure, which may easily lead to atrophy of the kidney parenchyma and cause damage to kidney function. Symptoms such as polyuria, oliguria, generalized swelling, hypertension, hypoproteinemia, etc. may occur. The situation of hydronephrosis triggering infection, which may form abscess kidney or pus accumulation in kidney, are very dangerous. It is recommended to have regular medical checkups and a yearly urological ultrasound to be able to detect some hidden conditions that have been clearly identified and to be treated in time to avoid aggravation of the condition and kidney failure.