The purpose of this paper is to understand characteristics of flow around I-beam, which is designed based on structural point of view. The flow is investigated by analyzing the influence of angle-of-attack on the vortex-shedding frequencies and the flow structures. To achieve this purpose, two-dimensional flow around circular cylinder, square cylinder and I-beam is calculated and proper orthogonal decomposition is applied to the results to extract flow structures. The results show that the cavity of I-beam has impacts on the flow and the flow becomes complicated especially at 45°.