Abstract: Flow-induced vibrations of cylinders with different cross-sections were investigated by employing a CFD numerical simulation at . The cylinders’ motion was modeled by a mass-spring-damper system. The flow field was calculated using Fluent software and the vibration equation of the cylinder was solved by the Newmark- method, which was manually written into a User-Defined-Function (UDF). The nonlinear coupling interactions between the cylinder and the flow field were studied through a dynamic mesh model. The influence of the different cross sectional shapes to the forms of vibration was investigated. The circular and hexagonal cylinders exhibit vortex-induced vibrations in the whole range of the frequency ratio. For the square and triangle cylinders, the vibrational form changes from ‘galloping’ to vortex induced vibration as the frequency ration increases, and the critical frequency ratio is captured. When the influence of streamwise vibration on transverse vibration was taken into consideration, the locus of the cylinder’s centroid is obtained and the results show that transverse vibration of the cylinder takes predominance. The present paper discusses the characteristic values of the aerodynamic force coefficient, the cylinder’s displacement, and the vortex structures in the wake region. The ‘beat’ and ‘phase switch’ phenomenon are captured and the feasibility of this numerical method is confirmed.