There are many causes of left renal sinus-like rounded low density shadow, such as renal cyst, benign or malignant tumor of kidney. We should pay attention to find the cause of the disease and choose different treatments according to the different causes, the main methods include surgery, radiotherapy and so on. If the left renal sinus-like rounded low-density shadow is a renal cyst, it can be diagnosed by ultrasonography. For those who are asymptomatic and without complications, the examination is repeated once every six months to one year. For large cysts with a diameter of >5cm, puncture aspiration and injection of sclerosing agent such as anhydrous ethanol can be considered to prevent recurrence. Surgery should be considered for patients with huge cysts >500ml in volume, malignant tendency or recurrence after puncture. If the left renal sinus-like rounded low-density shadow is a solid tumor, further renal enhancement CT or ultrasonography is needed to clarify the nature of the tumor. Benign tumors can continue to be observed. If it is a malignant tumor, it needs to be treated according to the specific situation, such as surgical treatment, radiotherapy, chemotherapy and so on. If the patient found the left renal sinus round low density shadow, it is recommended to go to the regular hospital in time, improve the examination to clarify the cause of the disease, and then give targeted treatment or treatment under the guidance of the doctor.