Abstract: Objective To compare the imaging features and difference of hypervascular early-stage ultra small renal cell carcinoma(usRCC) and angiomyolipoma with minimal fat(mfAML), and to improve the accuracy of differential diagnosis. Methods The CT images of hypervascular usRCC(47 cases) and hypervascular mfAML(22 cases) both with diameter of 2 cm or less confirmed by pathology in Cancer Hospital of University of Chinese Academy of Sciences(Zhejiang Cancer Hospital) from January 2014 to May 2019 were compared and analyzed retrospectively, including traditional imaging features and CT dynamic enhanced parameters, meanwhile receiver operating characteristic curves were drawn to evaluate the diagnostic efficacy. Results Traditional imaging features: the sex, cystic degeneration or necrosis, pseudocapsule sign, and enhance uniformity in parenchymal phase had significant differences between usRCC and mfAML(all P<0.05); the age, shape, location, tumor central point, wedge sign, cortex set off sign, black star sign, enhance uniformity in cortical phase and enhancement mode had no significance difference between usRCC and mfAML(all P>0.05). CT dynamic enhanced parameters: the CT value, NEV and REV of usRCC were all higher than those of mfAML in both cortical phase and nephrographic phase(all P<0.01). The area under the ROC curve was 0.748, 0.779, 0.787, 0.844, 0.800 and 0.789, respectively. The sensitivity and specificity of RCC were 85.1% and 77.3% respectively when the NEV of nephrographic phase was 73.6 as the critical value. Conclusion Morphological features in the traditional diagnosis of small renal carcinoma(diameter of 4 cm or less) have certain significance in differentiating hypervascular usRCC and mfAML at the early stage, but the diagnostic efficacy was limited. The CT quantitative parameters have relatively important value in differential diagnosis, among which the NEV in nephrographic phase have better diagnostic efficacy.