At present, CT scan is the best method to detect and qualitatively diagnose small kidney cancer, and multi-layer spiral CT (MSCT) further makes up for the shortcomings of single-layer SCT, with faster sampling speed, it only takes 0.5S for the bulb to rotate for one week and acquire four or more layers of images, and it only takes a few seconds to complete the whole kidney scan, and the scan time difference between the upper and lower pole of the kidney cancer foci is basically negligible. 2mm thin layer scan, it can not only improve the density resolution, correctly locate and show tumors with 0.5-1.0CITI or even smaller diameter, but also accurately reflect the enhancement characteristics of the lesions, which can characterize the pathological histological subtypes of most renal cancers. 1, renal cell carcinoma: typical tumor presents as a heterogeneous mass in the renal parenchyma with heterogeneous enhancement and lower density compared with normally enhanced renal parenchyma). Cystic renal cell carcinoma can be distinguished from benign cysts by its own irregular thick wall and tumor nodules. Renal cancer metastasis is typically located within the renal vein, in the para-aortic lymph nodes and in the renal interstitium. 2.Renal lymphoma: renal lymphoma is always the result of hematogenous dissemination and has various manifestations on CT, most commonly renal enlargement with some other changes, such as bilateral focal masses, obvious masses on one side or direct invasion of adjacent areas. Lymphoma manifestations are difficult to distinguish from renal cell carcinoma. Microscopic lesions can be more easily detected during spiral CT scan. 3.Renal angiomyolipoma: It is a limited misshapen tumor, mostly seen in middle-aged women or patients with tuberous sclerosis. Spiral CT scan can help to detect the tiny fatty foci within the renal mass, which is considered to be the characteristic manifestation of angiomyolipoma. 4. Metastases: It accounts for about 5% of renal tumors. Patients have hematuria. the combination of CT and intravenous urography has a significant role in determining the stage of metastases. During renal spiral CT scan, attention should be focused on the presence or absence of filling defects in the renal pelvis and collecting system. Delayed scanning of the renal pelvis and ureter must be completed for any minor intracavitary filling defect manifestations or in the examination of patients with known metastases. Delayed scanning can improve the detection rate and detailing of metastases. Other tumors: Other tumors that invade the kidney are diverse, and Wilms’ tumor is the most common. It usually presents as a large mass that may involve the renal vein and the inferior vena cava and collateral vessels. Three-dimensional reconstruction can accurately demonstrate the extent of the tumor. The presentation of giant eosinophilic granuloma is generally the same as that of renal cell carcinoma, but the diagnosis is supported by the presence of strips of hypointense non-enhancing areas due to scar formation in the center of the lesion. The specificity of SCT in diagnosing renal cancer is 95%, the accuracy is 95%, and the staging accuracy is 91%; the sensitivity of SCT in diagnosing renal vein and inferior vena cava tumor thrombosis is 85%, the specificity is 98%, and the accuracy is 96%. For kidney cancer with diameter greater than 3cm, the sensitivity of SCT in detecting clear cells is 80.2% and that of non-clear cells is 80.7%. Disadvantages of CT examination: there is X-ray radiation, the possibility of contrast allergy, some adenomas or eosinophilic tumors or pseudo-enhanced small renal cysts may be misdiagnosed as small renal cancer, and showing intraventricular cancer thrombus is not as good as MRI examination.