Small kidney cancer refers to malignant tumors less than 4cm in the kidney detected by imaging examinations, such as ultrasound and CT. In principle, small kidney cancer can be treated by preserving the kidney unit, that is, not removing the kidney but only removing the kidney cancer tissue, which can save the kidney function to the greatest extent and the possibility of acute renal failure after surgery is greatly reduced. Through long-term clinical observation, partial resection of kidney cancer less than 4cm is found to have no significant improvement in long-term survival compared with performing total kidney and tumor tissue resection, so kidney preservation therapy can be performed for patients with small kidney cancer. Epidemiology also found that after partial resection of small kidney cancer, the probability of recurrence of metastasis in the long term is the same as that after total resection of the same kidney, but the patients have retained part of the kidney, especially those with poorer contralateral kidney function have more benefits, so the treatment of small kidney cancer is slightly different from that of kidney cancer.