Left kidney density shadow 1cm, belongs to a kind of small internal kidney mass, means it may be kidney cyst or kidney tumor, the specific cause needs further analysis. 1. Kidney cyst: low density shadow of left kidney is usually observed during ultrasonography or CT examination, and cysts are more common. It is necessary to observe whether the cyst is calcified, whether it causes stones or bleeding, whether the cyst fluid is clear and whether there are new organisms in the cyst to determine the nature of the cyst. 2. Renal tumor: it can also cause hypodense shadow. In order to distinguish it from renal cancer, it is necessary to receive enhanced CT examination, and if necessary, it is necessary to receive puncture biopsy and differential diagnosis according to pathological examination. It is recommended that patients with abnormal density shadow of left kidney should consult regular hospitals and be treated under the guidance of specialists, avoiding blindly using medicines on their own to avoid aggravating the condition.