Abstract: Fluid flows through a rotating cylinder will form an asymmetric flow field, which often involves a variety of complex flow phenomena. Therefore, it is of great significance to study the velocity change of the rotating cylinder flow field and accurately capture the dominant mode of the velocity field for in-depth analysis of the flow field characteristics. Based on the Dynamic mode Decomposition (DMD) method, the velocity field of rotating cylindrical flow is studied. The flow field of a rotating cylinder is numerically simulated under uniform incoming flow and Reynolds number Re=130000. The flow field is decomposed by DMD, and the dominant mode is extracted to reconstruct the original flow field, which verifies the accuracy and effectiveness of the proposed method. The results show that the first 10 modes of DMD can accurately reconstruct the original flow field characteristics, the higher-order modes around the cylinder show a more complex structure, and the vortex position near the cylinder will change with the rotation of the cylinder.